Methyl Group 1 3 Diaxial Fashion

Cyclohexane Ring

To flip a cyclohexane ring, we hold the four "eye" atoms in identify while pushing 1 "end" carbon downward and the other upwardly.

From: Principles of Organic Chemistry , 2015

Conformations of circadian, fused and bridged ring molecules

Anil V. Karnik , Mohammed Hasan , in Stereochemistry, 2021

viii.13.2.ane Geometry

Both the cyclohexane rings in cis-decalin are in chair conformation. The ring fusion is through axial-equatorial bonds of both the cyclohexane rings. The cis-decalin has a folded structure. The ii faces of cis-decalin are different, the convex and the concave faces. The steric interaction (Bucourt, 1974) between hydrgens at C_ii, C_four, C_vi and C₈ tin can be seen on the concave face. The torsion angle at the band junction is +55 to +56° or −55 to −56° on the 2 sides. The ring-fusion geometry and the torsion angle at the band junction, tin can be more effectively viewed in Neman projection, shown in Fig. 8.42.

Figure 8.42. Cis-decalin geometry, ring inversion, extra-annular gauche-butane units and steric interaction between hydogens at C_ii, C_two, C₆ and C₈.

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Alkanes and Cycloalkanes Structures and Reactions

Robert J. Ouellette , J. David Rawn , in Organic Chemistry Study Guide, 2015

iv.viii Conformations of Monosubstituted Cyclohexanes

Substituents bonded to the cyclohexane ring take a conformational preference for the equatorial position. Substituents in the centric position are sterically hindered to some degree because they are within the van der Waals radii of the axial hydrogen atoms at the C-3 and C-v positions. This interaction is chosen a i,3-diaxial interaction.

The free energy differences between the axial and equatorial conformations of monosubstituted cyclohexanes are listed in Table 4.v. These values correspond the magnitude of the two 1,3-diaxial interactions, and they depend on the size of the atom, the length of the bond, the polarizability of the atom, and the number of atoms bonded to the cantlet directly bonded to the cyclohexane ring.

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Transition Metal Organometallics in Organic Synthesis

Douglas B. Grotjahn , in Comprehensive Organometallic Chemistry II, 1995

7.three.8 Cyclohexenes and Cyclohexanes

Straight synthesis of cyclohexene or cyclohexane rings by cyclooligomerization of an alkyne and two alkenes, or of 3 alkenes, respectively, could be a powerful synthetic tool. However, an illustration of the problems encountered is provided past the reactions of cobaltacyclopentane ( 144 ) ¹⁵⁹ (Scheme 29). As with other metallacyclopentanes, peculiarly of late transition metals, thermolysis of ( 144 ) at room temperature gives i-butene, whose origin is ascribed to β-hydride elimination/reductive emptying, and two-butenes, from metallic-catalyzed isomerization of the alkene office. Interaction of ( 144 ) with CO gives a cyclic ketone, but reaction with ethyne or ethene leads to ane,5-hexadiene or 1-hexene, consistent with decomposition of intermediate cobaltacyloheptene or cobaltacycloheptane by β-hydride elimination/reductive elimination.

Scheme 29.

Thus, special alkenes or dienes in which β-hydride emptying from metallacyclic intermediates is blocked seem to exist the simply reported participants in successful cyclotrimerization. Perhaps the virtually spectacular example is 3,iii-dimethylcyclopropene, which dimerizes in the presence of some Ni⁰ catalysts but trimerizes to ( 145 ) in most quantitative yield under Pd(PPh₃)_iv catalysis (Scheme 30). ¹⁶⁰ Under nickel catalysis, 3,three-dimethylcyclopropene could be induced to enter into cotrimerization with methyl propenoate to produce ( 146–148 ); variation in phosphine ligands allows one to increase the proportion of any of the three products to at least 65% of the mixture. ¹⁶¹ Ii molecules of propadiene combine with 1 of ethyne using Ni⁰ catalysts to class ( 149) and (150 ), ¹⁶² selectivity existence possible past variation of ligands. i,ii,3-butatriene derivative ( 151 ) may be induced to trimerize or dimerize under the appropriate weather condition. ¹⁶³ Norbornadiene undergoes [ii   +   2   +   two] cyclization with alkenes and alkynes under nickel and cobalt catalysis. Since cyclization with unsymmetrical alkynes produces 6 new chiral centers in the product, enantioselective versions of the processes accept been developed, with the goal of using adduct ( 152 ) every bit a starting material for organic synthesis. ¹⁶⁴

Scheme xxx.

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Alkanes and Cycloalkanes

Robert J. Ouellette , J. David Rawn , in Organic Chemistry, 2014

4.8 Monosubstituted Cyclohexanes

We have seen that when a cyclohexane band flips, all equatorial bonds get axial and all axial bonds become equatorial. Now allow's consider the consequences of flipping a substituted cyclohexane ring. The chair–chair interconversion of monosubstituted cyclohexanes occurs very chop-chop. All the same, the two conformations of monosubstituted cyclohexanes, unlike those of cyclohexane, are not as stable.

Let's consider methylcyclohexane in a chair conformation with an equatorial methyl grouping. When the ring flips, the equatorial methyl group moves into an axial position (Figure 4.fourteen). These two structures are different conformations, not structural isomers. A methyl group in an axial position is eight.1   kJ mole^{−   1} less stable than a methyl group in an equatorial position. At equilibrium, near 95% of the mixture has an equatorial methyl group.

Figure 4.xiv. Conformations of Methyl Cyclohexane

Methylcyclohexane rapidly interconverts between two conformations of diff free energy. At room temperature, 95% of the conformations have an equatorial methyl group and v% have an axial methyl group. The axial conformation has unfavorable interactions with axial hydrogens at C-3 and C-3′.

The conformation with an axial methyl group is less stable than the conformation with an equatorial methyl group considering an axial methyl grouping experiences steric strain from centric hydrogen atoms at C-3 and C-v. This ane,3-diaxial strain is coordinating to the steric repulsion between two methyl groups in the gauche conformation of butane. The same relationship occurs twice in the axial conformation of methylcyclohexane (Figure 4.fifteen). When we examine the C-one to C-ii bond, we come across that the methyl group is at a lx° dihedral angle to C-3. A similar relationship exists between the methyl group and C-5 when the view is along the C-1 to C-half dozen bond. In the equatorial conformation, the methyl group is anti to both C-3 and C-five. Therefore, the steric strain for the centric conformation of methylcyclohexane is twice that of the gauche interaction of butane or 2   ×   3.viii   =   7.6   kJ mole^{−   one}.

Figure iv.15. one,three-Diaxial Interactions in Methylcyclohexane

An axial methyl grouping is at a 60° dihedral angle with respect to the methylene groups at C-3 and C-5. This interaction is equivalent to two gauche butane interactions. Sighting down the C-one to C-half-dozen bond shows the eclipsing of the methyl group by the C-5 axial hydrogen cantlet.

The conformational properties of other substituted cyclohexanes are similar. That is, the conformation with an equatorial substituent is ever more than stable than the conformation with an centric ane. The conversion of an equatorial to an axial conformation is an unfavorable procedure. The free energy difference depends upon the identity of the substituent and is called its conformational preference. A listing of these energy differences is given in Table four.6. The conformational preference of a substituent on a cyclohexane ring—that is, the magnitude of the one,3-diaxial interaction—reflects its interaction with the cyclohexane band. The conformational preferences of a methyl grouping, hydroxyl group, and fluorine atom decrease in the order CH_three  >   OH   >   F. This trend reflects in role the decrease in atomic radii from left to right in the periodic table. The conformational preferences of methyl, ethyl, isopropyl, and t-butyl subtract in the gild (CH₃)₃C   >   (CH₃)₂CH   >   CH₃—CH₂  >   CH₃. The trend reflects the ease with which the alkyl group tin can be oriented in an equatorial site compared to an axial site. This trend parallels the "size" of the alkyl group, which corresponds to its van der Waals radius.

Table 4.half dozen. Conformational Preferences of Groups

Group	Strain energy (kJ mole−   1)
CN	0.8
F	one.0
Cl	2.viii
OH	iv.2
CH3	vii.six
CHthree─CHtwo	8.0
(CH3)2CH	9.ii
(CHiii)3C	22
CO2H	5.eight

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Stereochemical Concepts

Dipak K. Mandal , in Pericyclic Chemistry, 2018

2.1.3 Cyclic Conformation

The preferred cyclic conformation of a cyclohexane ring is chair conformation with axial (a) and equatorial (e) bonds ( Fig. two.4). The drawing of a chair indicates the joining of staggered sawhorse structures. Note the Yard- and Westward-shapes (highlighted in bold in a separate cartoon) for equatorial bonds at C-6, C-2 and at C-5, C-3, respectively.

Fig. 2.iv. Chair conformation of cyclohexane.

In that location are two possible chair conformations for a substituted cyclohexane equally shown with a trans-1,2-disubstituted cyclohexane in Fig. ii.v. Note the upwards/down relationship of substituents which is maintained throughout. Here the two chair conformations are distinguishable as (a, a) and (e, east) conformations.

Fig. two.5. Planar representation and chair conformations of trans-i,ii disubstituted cyclohexane.

Pericyclic reactions such as Cope and Claisen rearrangements ordinarily involve a chair transition structure. The ii possible chair transition structures from an acyclic substrate can be easily fatigued by either Method 1 or Method ii every bit delineated in Fig. two.half-dozen. In each method, the eclipsed wedge formula is translated into a staggered sawhorse structure that straightway leads to the chair transition structure. The up/downwardly substituents are maintained throughout the process.

Fig. 2.vi. Drawing of two possible chair transition structures starting from an acyclic substrate.

In the bicyclic decalin arrangement, two chair conformations can be trans fused (cf. trans-1,two-dimethylcyclohexane) or cis fused (cf. cis-i,2-dimethylcyclohexane) (Fig. 2.7). Such a two-chair bicyclic transition structure is likewise involved in pericyclic processes.

Fig. 2.7. 2-chair conformations of trans-decalin and cis-decalin.

Besides chair conformation, pericyclic reactions can also proceed through the gunkhole transition construction. The boat conformation of cyclohexane is drawn in two equivalent representations in Fig. 2.8. a′ and east′ denote pseudoaxial and pseudoequatorial bonds, respectively. The flagpole bonds at C-1 and C-4 are indicated.

Fig. 2.8. Boat conformation of cyclohexane.

The ii possible boat conformations of the transition construction from an acyclic substrate tin be fatigued equally shown in Fig. 2.9 (cf. Method 2 of Fig. two.6). The eclipsed wedge formula is translated into an eclipsed sawhorse representation that directly gives gunkhole transition structures. The up/down substituents are maintained throughout.

Fig. two.nine. Cartoon of two possible boat transition structures from an acyclic substrate.

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Ionic reactions one: Fundamental stereochemistry

Dipak 1000. Mandal , in Stereochemistry and Organic Reactions, 2021

6.2.2 E2 emptying in cyclic systems ^28,29

In cyclohexyl systems, the required antiperiplanar conformation of the departing groups in E2 elimination is the chair diaxial conformation (see Fig. 4.9B). Fig. 6.16A shows that anancomeric cis-4-t-butylcyclohexyl tosylate undergoes E2 elimination readily with base but the trans isomer does non. Since in the cis isomer, OTs and H on adjacent carbons are diaxial (antiperiplanar), E2 elimination takes identify readily to requite four-t-butylcyclohexene. Notation that the conformation of the cyclohexene production will exist half-chair. But in the trans isomer, OTs and H are diequatorial (east,e) or equatorial-axial (e,a), and E2 does non occur.

Fig. 6.sixteen. E2 eliminations with (A) cis- and trans-4-t-butylcyclohexyl tosylates and (B) cyclohexyl tosylate.

Cyclohexyl tosylate itself undergoes the E2 elimination slower than the cis isomer of 4-t-butylcyclohexyl tosylate (k/thou _cis   =   0.26 where k and m _cis are the rate constants for cyclohexyl tosylate and the cis isomer respectively) (Fig. 6.16B). Using the Winstein–Holness equation (see Section 5.ane.i),

$m={\mathrm{ten}}_{\mathrm{eastward}}{k}_{\mathrm{due\; east}}+x_{\mathrm{a}}{k}_{\mathrm{a}}={\mathrm{10}}_{\mathrm{a}}{m}_{\mathrm{a}}\left(\text{since}{m}_{\mathrm{e}}=0\right)=0.326k_{\mathrm{a}}$

$k_{\mathit{cis}}=x_{\mathrm{a}}{k}_{\mathrm{a}}={\mathrm{yard}}_{\mathrm{a}}\left(\text{since}{\mathrm{ten}}_{\mathrm{a}}\approx \mathrm{ane}\right).$

Thus, k/grand _cis   =   0.326, which agrees reasonably well with the experimental value.

Fig. 6.17 shows that diastereomeric neomenthyl chloride and menthyl chloride (differing in the stereochemistry of Cl) undergo E2 dehydrohalogenation differently with respect to reactivity and product limerick nether the same conditions with base of operations. Neomenthyl chloride reacts 250 times faster than menthyl chloride and gives a iii:ane mixture of 3-menthene and 2-menthene, whereas menthyl chloride produces only 2-menthene. Neomenthyl chloride tin react via its well-nigh populated (lowest energy) conformer in which Cl and H are antiperiplanar (Fig. 6.17). In contrast, the all-equatorial lowest energy conformer of menthyl chloride in which Cl and H are not antiperiplanar, is unreactive. Band flipping can produce the all-axial conformer which is much higher in energy but only in this conformer can E2 dehydrochlorination take identify. Since the concentration of the reactive conformer of menthyl chloride is low, its rate is much lower than that of neomenthyl chloride. In the example of neomenthyl chloride, there are 2 antiperiplanar protons (labelled H^a, H^b) that can be eliminated producing two alkenes with a preference for the more substituted Saytzeff alkene (3-menthene). Merely the reactive conformer of menthyl chloride has only ane antiperiplanar proton for removal by base giving a single alkene (2-menthene).

Fig. six.17. E2 eliminations of neomenthyl chloride and menthyl chloride.

The dissimilar stereochemical grade of E2 eliminations of ii diastereomeric carboxylic acids is depicted in Fig. vi.18A . The cis acid undergoes dehydrobromination as Br and H are merely antiperiplanar. But in the trans acid, since Br is also antiperiplanar with ${{\mathrm{CO}}_{\mathrm{ii}}}^{-}$ , decarboxylation takes place as it is expected to be faster than dehydrobromination.

Fig. 6.18. (A) Stereochemical course of E2 elimination of two diastereomers of two-bromo-five-t-butylcyclohexanecarboxylic acid; (B) Iodide induced elimination of cis- and trans-i,2-dibromocyclohexanes.

Fig. half dozen.18B shows that both cis- and trans-i,2-dibromocyclohexanes on treatment with iodide requite cyclohexene. For the trans isomer, the E2 debromination takes identify readily from the antiperiplanar diaxial (a,a) conformation but the (east,a) conformer of the cis isomer cannot undergo E2 elimination direct. The kinetic studies evidence that the cis isomer reacts well-nigh 11.five times slower than the trans isomer. Presumably, the cis dibromide undergoes an S_Ntwo reaction in a slow, rate-determining footstep followed by a fast diaxial (a-I,a-Br) elimination.

If the departing groups could not attain antiperiplanarity, syn elimination can take identify. For example, elimination from the deuterated norbornyl bromide (X   =   Br) or deuterated norbornyl trimethylammonium ion ( $\mathrm{X}={{\mathrm{NMe}}_{\mathrm{three}}}^{+}$ ) with base is syn (Ten and D are synperiplanar), and gives norbornene containing no deuterium (Fig. 6.19). ^30,31 Here the rigid ring system prohibits antiperiplanarity. Furthermore, there will be a steric constraint for the removal of the endo proton. In general, NMe₃ ⁺ has a greater trend for syn elimination than do other groups such as Br, Cl and OTs.

Fig. vi.nineteen. syn Elimination in norbornyl systems.

Finally, it should exist noted that cyclohexane rings are the most important rings for antiperiplanar E2 eliminations, and other rings are not then selective. For example, in the decomposition of cycloalkyltrimethylammonium hydroxides, the extent of syn emptying with ring size is: four-membered (90%), five-membered (46%), half dozen-membered (4%), vii-membered (31%–37%). ³²

Problem 6.7

I diastereomer (β) of 1,two,3,4,5,6-hexachlorocyclohexane undergoes HCl elimination with base of operations 7000 times slower than the slowest of the other seven diastereomers. Identify the β isomer.

Problem 6.8

Which of the following bromides would eliminate HBr with base? Explain.

Problem 6.9

Business relationship for the following observations:

(a)

The compound A undergoes HCl elimination much slower than the corresponding nonbridged compound.

(b)

The chemical compound B undergoes HCl emptying well-nigh 8 times faster than the compound A.

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Alkanes and Cycloalkanes: Structures and Reactions

Robert J. Ouellette , J. David Rawn , in Organic Chemical science (Second Edition), 2018

Drawing Cyclohexane Rings

We tin draw the carbon skeleton of a cyclohexane ring with three sets of parallel lines having unlike slopes. To practice this, we proceed as follows.

ane.

Describe one gear up of parallel lines that slant slightly downward. These are the "seat" of the chair. This orientation matches the chair conformations shown in Figures 4.9 and 4.10. The carbon atoms stand for to bonds from C-2 to C-3 and from C-5 to C-6.

2.

Second, place C-i above and to the right of C-two. Connect C-1 to C-6.

3.

Third, place C-4 to the left and below C-three. Then, connect C-3 and C-5 to C-4.

When nosotros look at this process, we encounter that we have iii sets of parallel lines:

ane.

The lines joining C-3 to C-2 and C-v to C-6 are parallel.

two.

The lines joining C-1 to C-2 and C-iv to C-v are parallel.

three.

The lines joining C-three to C-4 and C-ane to C-6 are parallel.

Having drawn the carbon skeleton, we next add the axial and equatorial bonds. It is easy to draw the axial bonds. Beginning at C-1 get around the band with alternating up and downwards lines. Up bonds are at C-one, C-iii, and C-5; downwardly bonds are at C-2-, C-4, and C-half-dozen.

It is not quite every bit like shooting fish in a barrel to draw the equatorial bonds. Similar the bonds in the ring itself, we can depict them as three sets of parallel lines.

1.

The lines for the equatorial bonds at C-1 and C-four are parallel.

two.

The lines for the equatorial bonds at C-2 and C-v are parallel.

iii.

The lines for the equatorial bonds at C-3 and C-6 are parallel.

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STEREOCHEMISTRY AND THE Chemical SHIFT

L.Chiliad. JACKMAN , Southward. STERNHELL , in Application of Nuclear Magnetic Resonance Spectroscopy in Organic Chemical science (Second Edition), 1969

K THE CHEMICAL SHIFTS OF AXIAL AND EQUATORIAL PROTONS AND GROUPS ATTACHED TO Vi-MEMBERED RINGS IN CHAIR CONFORMATION

In the absence of complicating factors, equatorial protons in the cyclohexane band requite rise to resonances downfield from their axial counterparts. Some examples of this are listed in Table iii-8-8 and others are given in references listed on pp. 290–365, while a very extensive list of references tin can be establish in a review by Franklin and Feitkamp. ⁸⁸²

Table iii-eight-viii. Chemic SHIFTS OF Axial AND EQUATORIAL PROTONS IN CYCLOHEXANE DERIVATIVES

a From low temperature spectra

b See besides references listed in Table 1 of ref. 882. Information for several pairs of iv-t-butyl derivatives are listed in ref. 746.

The chemical shifts listed in Tabular array iii-eight-8 were obtained either from spectra taken at low temperatures, nether which conditions conformational inversion is sufficiently dull to permit observation of the superimposed spectra due to the separate conformers, or by the method of "reasonable fixed models", in this case the 4-t-butyl derivatives. It tin can be seen that, whenever straight comparing is possible, the values obtained past means of the ii methods are in reasonable agreement, ^{744, 882} peculiarly equally the details of experimental conditions (e.g. concentration) were in full general not identical. Withal, with some substituents the possibility of serious distortion cannot exist excluded. ¹¹⁴

The principal utility of data of this blazon has been in investigating conformational equilibria in monosubstituted cyclohexane derivatives and related systems ^{744, 882, lxx} where the average chemic shift observed under the conditions of rapid conformational equilibrium can be just related to the proportions of the private conformers present (cf. Capacity 2-1 and 5-1). An analogous method employing averaged vicinal coupling constants is too oft utilized (Affiliate 4-two).

For routine stereochemical assignments, the correlation embodied in Table 3-8-8 should exist used with caution, firstly because fifty-fifty the relatively minor influences of many common substituents on β- or γ-carbon atoms are oftentimes of the same order of magnitude as the differences between axial and equatorial shifts (cf. preceding section), and secondly because some substituents can exert pronounced long-range effects which are capable of inverting the usual lodge.

The almost important instance of such an inversion is the full general observation of the resonances due to equatorial α-protons in α-halocyclohexanone derivatives at higher fields than those due to their axial counterparts ^{952, 2521} , ^{1873, 954} [cf e.yard (xxi) ²⁵²¹ and (XXII) ⁹⁵² ] although in some compounds ¹⁵ the differences between them are negligible.

The aforementioned inversion may be observed in the spiro-compound (XXIII), ²⁴⁵³ the pair of decalones (XXIV) and (XXV), ¹²²¹ in some steroidal ketones ²³⁸ and in other compounds. ^{1547, 1557, 2280, 2375} The chemical shifts of both protons and acetyl groups in many flavan derivatives ⁴⁹⁴ are subject to then many relatively stiff influences that little stereochemical information tin exist gained, although a large number of related compounds accept been examined. ^{494, 1710}

It is interesting that the axial and equatorial homoallylic protons in cyclohexene ^{104, 947} which requite rise to a resonance at ane·65 ppm in the rapidly inverting mixture at room temperature, appear to be separated by approximately 0·4 ppm at depression temperature, a value non greatly different to that in cyclohexane itself.

Since the early piece of work past Lemieux, Kullnig, Bernstein and Schneider, ¹⁵³⁹ many attempts have been made to correlate the chemical shifts of protons in the functional groups fastened to six-membered rings (principally cyclohexane and pyranose monosaccharides) with their configuration, and a number of such correlations are summarized in Table three-8-nine. It can exist seen that exceptions have been observed and hence assignments should be based on closely related compounds. In the case of the hydroxyl grouping, studies past Ouellette ^{1920, 1923, 1922} indicate that their chemical shifts at high dilution in carbon tetrachloride appear to exist little affected past their environment.

Table 3-8-ix. CHEMICAL SHIFTS AND CONFIGURATION OF FUNCTIONAL GROUPS Fastened TO Vi-MEMBERED RINGS IN THE CHAIR CONFORMATION

Group	Relationship a	References	Exceptions (references)
–O–CO–CHiii	Equatorial upfield	1539, 1232, 1086, 1554, 2331, 1566, 141, 1565, 1564	155
–NH–CO–CH3	Equatorial upfield	1566, 1565
–OCH3	Axial upfield	114, 141	993, 155
–CH3	Equatorial upfield b	1289, 1290
–OH	Axial upfield	2415, 2220, 464, 1920, 1922, 1965, 445, 1923	2220
–OSi(CH3)3	Equatorial upfield	1308

a

The differences are more often than not 0·1–0·ii ppm except in the case of hydroxyl groups where they may achieve 0·v ppm. The ranges generally overlap.

b

Cyclohexanone derivatives.

In saturated six-membered heterocyclic compounds in that location is the boosted possibility of different steric relations to the heteroatoms which may have long-range furnishings on chemical shifts (Chapter 2-two). A large amount of data are available for the pyranose carbohydrates, ¹⁰⁸⁵ some of which are quoted in Tabular array 3-8-9, and data for other systems are given in Table three-8-ten. Information technology tin can be seen that, while the general relationship observed for cyclohexane derivatives appears to apply in about cases, in systems containing nitrogen big differences between the chemical shifts of centric and equatorial protons can be observed which should prove very valuable in stereochemical assignments.

TABLE iii-8-10. Chemic SHIFTS OF AXIAL AND EQUATORIAL PROTONS IN SOME SATURATED HETEROCYCLIC COMPOUNDS

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CHEMICAL FINGERPRINTING METHODS

Gregory S. Douglas , ... Kevin J. McCarthy , in Introduction to Environmental Forensics (Second Edition), 2007

9.4.6 DIAMONDOID Analysis Past DIRECT INJECTION GC/MS

Diamondoids are volatile saturated hydrocarbons that consist of three or more fused cyclohexane rings, which results in a cage-like or diamond-similar construction ( Fort and Schleyer, 1964; Fort, 1976)—hence, their course proper noun (run into Figure 9.12). The addition of various alkyl side bondage (e.yard., methyl- and ethyl-groups) yields a series of substituted diamondoids within each parent diamondoid group. For case, addition of a methyl grouping in a bridgehead or secondary position on adamantane (meet Figure 9.12) produces i-methyladamantane or two-methyladamantane, respectively. Diamondoids have been demonstrated to be quite resistant to even severe levels of biodegradation of reservoired petroleum over geologic time scales (Williams et al., 1986; Grice et al., 2000). By extension, their resistance to biodegradation would exist anticipated for diamondoids found in petroleum released (or spilled) in the nearly-surface surround. Equally such, the relative abundance and chemical distribution of diamondoids in light petroleum products in the environment offers significant promise as a fingerprinting tool.

Effigy ix.12. Molecular structures for iv parent (nonsubstituted) diamondoids;

(A)

adamantane,

(B)

diamantane,

(C)

triamantane, and

(D)

iso-tetramantane. Hydrogen atoms omitted for clarity.

The presence and distribution of diamondoids in petroleum mostly has been observed using gas chromatograph-mass spectrometry (GC/MS) on the whole oil or aliphatic hydrocarbon fraction of oil. Examples of GC/MS programs used to analyze for these compounds are provided in Table ix.8. The overall stability of these compounds (see before) results in predictable (electron touch on, 70 eV) mass spectra for parent diamondoids that exhibit a strong molecular ion (G+) base peak (a feature also characteristic of polycyclic aromatic hydrocarbons), whereas methyl- and ethyl-substituted diamondoids showroom base peaks of Thou⁺-xv and Thou+-29, respectively (Wingert, 1992; Chen et al., 1996). The elution order of the commonly recognized parent and alkyl-substituted adamantanes and diamantanes on nonpolar GC columns is quite well established (e.g., Wingert, 1992; Chen et al., 1996). On a nonpolar capillary cavalcade, adamantane is expected to elute just prior to n-C_eleven (see Figures 9.13 and 9.14) and diamantane is expected to elute betwixt n-C₁₅ and due north-C₁₆ (see Figures nine.xiii and 9.15). Based upon their elution relative to n-alkanes, the boiling points (BP) of adamantane and diamantane are estimated to be 190°C and 272° C, respectively (Wingert, 1992). Although chemical standards are available for some diamondoids (Chiron As, Norway), the predictable mass spectral and chromatographic behavior of adamantanes and diamantanes generally allows for confident identification of these compounds nether about GC/MS weather. NAPL and product samples have been analyzed using both direct injection methods discussed earlier with satisfactory results.

Figure ix.13a,b. Total ion chromatograms of (a) a natural gas condensate and (b) gasoline-derived NAPL showing intervals in which adamantanes and diamantanes elute (dashed lines). C10-due north-decane, T-toluene, Eastward-ethylbenzene, Ten-xylenes, 124TMB-1,2,iv-trimethylbenzene, N-naphthalene, MN-methylnaphthalenes.

Figure 9.14. Extracted ion profiles of a natural gas condensate showing the C₀ to C₄ alkylated adamantanes eluting in the n-C₁₁ to north-C₁₃+ range. For superlative identifications refer to Table nine.11.

Effigy 9.15. Extracted ion profiles of a natural gas condensate showing the C₀ to C₂ alkylated diamantanes eluting in the n-C₁₅ range. The low signal results from low, merely detectable, concentrations of diamantanes in this condensate. For peak identifications refer to Table nine.eleven

The identification of individual adamantanes and diamantanes is determined based upon comparison to published (relative) retentivity times and full scan mass spectra (east.g., Wingert, 1992). This same data is used to develop a data processing method that utilized various extracted ion chromatograms to determine relative concentrations (based upon manually integrated elevation areas) of the target compounds (or compound groups) listed in Table nine.11. Each target compound's base meridian area counts are used to determine the relative concentration.

Table 9.11. Inventory of adamantane, diamantane, due north-alkane and alkylbenzene target analytes and cardinal masses used in their identification and (relative) quantification via GC/MS. Height numbers are used in the figures.

Compound	Pk. #	Formula	M+	Base Peak
adamantane	1	C10H16	136	136
i-methyladamantane	2	C11H18	150	135
1,three-dimethyladamantane	3	C12H20	164	149
1,three,5-trimethyladamantane	4	CxiiiH22	178	163
1,3,five,vii-tetramethyladamantane	5	CfourteenH24	192	177
2-methyladamantane	6	C11Heighteen	150	135
1,iv-dimethyladamantane, cis	vii	C12Htwenty	164	149
1,four-dimethyladamantane, trans	8	C12Hxx	164	149
one,3,half dozen-trimethyladamantane	9	CxiiiH22	178	163
ane,ii-dimethyladamantane	10	C12H20	164	149
1,three,4-trimethyladamantane, cis	11	C13H22	178	163
1,3,4-trimethyladamantane, trans	12	C13H22	178	163
1,two,5,7-tetramethyladamantane	13	CxivH24	192	177
1-ethyladamantane	14	C12Hxx	164	135
ane-ethyl-3-methyladamantane	xv	C13H22	178	149
1-ethyl-3,5-dimethyladamantane	16	C14H24	192	163
2-ethyladamantane	17	C12H20	164	135
diamantane	eighteen	C14Htwenty	188	188
4-methyldiamantane	19	CxvH22	202	187
4,9-dimethyldiamantane	xx	C16H24	216	201
1-methyldiamantane	21	C15H22	202	187
one,4- and 2,four-dimethyldiamantane	22	C16H24	216	201
iv,8-dimethyldiamantane	23	C16H24	216	201
trimethyldiamantane	24	C17H26	230	215
three-methyldiamantane	25	C15H22	202	187
3,4-dimethyldiamantane	26	CxviH24	216	201
undecane	C11	C11H24	156	57
dodecane	C12	C12H26	170	57
tridecane	C13	CthirteenH28	184	57
pentadecane	C15	CxvH32	196	57
Full Cfive-alkylbenzenes			148	133

The retention time range of adamantanes and diamantanes in natural gas condensate (run across Effigy 9.13a) and in gasoline (come across Figure ix.13b) tin can also be determined past the techniques described here (Stout and Douglas, 2004). This group of chemicals are among the least impacted of the volatile range hydrocarbons by weathering processes (e.thousand., evaporation, volatilization, biodegradation). An example of extracted ion plots for C₀-C₄ alkylated adamantanes and C₀-C₂ alkylated diamantanes relative to the due north-alkane distribution are provided in Figures nine.14 and nine.15, respectively. These compounds elute in the north-C_eleven through n-C_fifteen carbon range, many outside the analytical range of the P&T GC/MS method.

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Eight-membered and larger Heterocyclic Rings and their Fused Derivatives, Other Seven-membered Rings

P. Hermann , J. Kotek , in Comprehensive Heterocyclic Chemistry III, 2008

14.11.three Experimental Structural Methods

Since 1995, more than 250 single-crystal Ten-ray structures of organic compounds (excluding their metallic complexes) relevant for this affiliate were deposited in the Cambridge Structural Database (CSD). Therefore, only cursory overview of the reported structures is given here.

14.11.iii.1 Structures of Mono- and Diazamacrocycles

The crystal analyses of N -BOC-azacyclododecane fused with substituted cyclohexane ring 13 <2005AGE6038>, N-indenyl azacyclotridecane 14 <1998JOM83>, protonated azacyclotetradecan-viii-one 15 (in malate or tartate salts) <1999JA2919>, and trifluoroacetate of azacyclohexadecane-based mutuporamine 16 <2002JOC245> were reported.

14.11.3.two Structures of Triazamacrocycles

1,2-Dichlorotetrafluorocyclobutene was reacted with macrocyclic amines introducing two-chloro-three,iii,iv,4-tetrafluorocyclobutenyl substituent on nitrogen atoms. Double-substituted 1,four,8-triazacycloundecane 17 and fully substituted one,5,nine-triazacyclododecane were analyzed by 10-ray diffraction. The report revealed planar arrangement around substituted nitrogen atoms due to the extreme electron-withdrawing effect <1998IC5342>. Single crystals of diprotonated Northward-benzyl-1,5,9-triazacyclododecane <1997TL1911> (protons are bound on both secondary amino groups) and monoprotonated (on ane of secondary amines) N-(p-vinyl)benzyl-1,5,nine-triazacyclododecane 18 <1999JP11621> in nitrate salts were analyzed. The construction of bis(macrocyclic) xix consisting of two 1,5,9-triazacyclododecane units bridged by a p-xylylene grouping was reported as the diperchlorate salt (each macrocyclic unit is protonated on one of the secondary amino groups) <1997TL1911>. One time-protonated macrocycles adopt a close inward construction, in which proton is bound in the cardinal cavity by intramolecular hydrogen bonds to the other nitrogen atoms, with short N–N distances around iii.0   Å. Contrariwise, diprotonation of the skeleton opens the cyclic courage (shortest intramolecular N–N distance ∼ 3.6   Å) and leads to intermolecular hydrogen bonding. A series of N,N′,Due north″-tritosylated i,v,9-triazacyclododecanes twenty substituted in C3 position by dissimilar benzyl groups was deposited in CSD by a personal communication <2000MI>.

14.eleven.3.iii Structures of Polyazamacrocycles with Four and More Nitrogen Atoms

A bulk of the crystal structures relevant for this affiliate belong to derivatives of cyclen 1 (ca. fifty structures) and cyclam 2 (ca. 130 structures). Among them, several structures of homocyclen 21 derivatives (homocyclen   =   i,4,7,x-tetraazacyclotridecane) and larger homocyclam 22 (homocyclam   =   ane,4,8,12-tetraazacyclopentadecane) and 1,5,nine,13-tetraazacyclohexadecane 23 derivatives have appeared.

The structural characteristics of cyclen and cyclam and their carboxylic and amidic derivatives in variously protonated states equally well as their metal complexes were excellently reviewed by Guilard and co-workers <1998CCR1313>. As those derivatives are oftentimes used in the complexation of transition metal or lanthanide ions, the space arrangement, exact protonation sites, and presence of intramolecular hydrogen bonds are of involvement from the point of view of kinetics of complex formation/dissociation. Since the number of related structures is very high, simply no new remarkable information appeared since Guilard's review, derivatives of these macrocycles are not discussed in detail.

The structure of monoperchlorate of 12,12-dimethyl-homocyclen was reported <1997AXC586>. The construction of the bis(macrocyclic) 24 where p-xylylene group bridges nitrogen atoms N1 of ii homocyclam units was reported <1997NCS129>. From sixteen-membered tetraaza-rings, Northward,N′,N″,North‴-tetramethyl-1,5,9,13-tetraazacyclohexadecane was structurally characterized <2004MI>.

Unproblematic one,4,7,ten,13,16-hexaazacyclooctadecane 25 (hexacyclen), used in anion complexation studies (see Department 14.eleven.8.2), was crystallized in differently protonated (four- or sixfold) forms as sulfate, hydrogen sulfate, chloride–hydrogen sulfate, dithionate <2004NJC1301>, chloride, bromide, iodide–triiodide <2004NJC1160>, several dihydrogen phosphates <2004IC6936>, dihydrogen diphosphate <1999JA6807>, differently protonated trifluoromethanesulfonates <1995AXC1407>, hydrogen oxalate–oxalate, trifluoroacetate, picolinate, and bis(p-nitrophenyl)phosphate <2005MI713>. In addition, structures of Northward-substituted derivatives, namely i,10-dimethyl derivative in the form of dihydrogen diphosphate salt <1999JA6807> and 1,ten-dimethyl-4,seven,13,16-tetrakis(2,3-dihydroxobenzoyl) derivative <1998JCD359>, were solved.

From larger macrocyclic rings, only the structures of i,four,7,10,13,16,19,22-octaazacyclotetracosane in fully protonated nitrate form <1999NJC1007> and its octa(N-acetate) derivative in the form of Bu^t ester <1997CB267> were reported.

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