Trans- and cis-configuration

Even though the atoms within a peptide bond are coplanar, they can exist in two possible configurations, cis and trans ... 

Polymerization can occur as a 1,2-addition or a 1,4-addition that is, the radical can attack a diene molecule with the free electron on either carbon 2 or carbon 4. This accounts for two possible polymerization products, but there is a third one. Note that the growing polymer in 1,4-addition can have two different configurations cis and trans. The radical can add to a diene by 1,4-addition to produce a trans or a cis product ... 

Surface species containing multiple CO ligands in different relative configurations (cis and trans) were hypothesized and discussed. The chemistry of Mn -Sn oxide system towards CO has also been investigated only the formation of labile a-type monocarbonylic structures was revealed by... 

Chain tacticity of tertiary carbon macromolecules Head-to-head, head-to-taU, and tail-to-tail configuration in polyvinyls Trans (the planar zigzag) versus gauche (a = 120°) configuration Cis and trans isomerism and 1,2- versus 1,4-addition of dienes... 

We shall see in Chapter 2 that the hybrid radical (A ) formed by reaction (8) and the resulting peroxyl radicals by reaction (9) can assume different stereochemical conformations, which determine the geometric configurations (cis and trans) of the isomeric hydroperoxides from various unsaturated lipids oxidized under different conditions. The oxygen addition reactions (8) and (9) can be reversible for many radicals. The reverse reaction (-9) proceeds by /J-scission or j8-fragmentation of the carbon-oxygen bond (-C-I-00 ) of the peroxyl radicals and may also determine the stereochemical configuration of the isomeric hydroperoxides,... 

Corcoran and collaborators (2007) studied the effects of various Cl 8 fatty acids with 0-2 bonds in the two configurations, cis and trans, on rate survival of a Lactobacillus rhamnosus GG strain, in the simulated acid conditions of gastric juice. The protective effects to the acidic environment was offered only by oleic and vaccenic acids [C18 1 (lit)] among elaidic, linoleic and stearic acids and two conjugated linoleic acid (CLA) isomers (Corcoran et al., 2007 Kankaanpaa et al., 2014). On the other hand, oleic acid increased the survival rate of a Lactobacillus rhamnosus strain, in 90 minutes after exposure to simulated gastric juice (by 1500-fold) compare to the control. Moreover, when the culture media was supplemented with... 

Dienes with tt electron conjugated double bonds, such as 1,3- butadiene and its derivatives undergo an addition process in both positions 1.2 and 1.4. As a result of the polymerization process of 1.2 type a polymer containing side vinyl groups is formed, while 1.4 addition reaction leads to a polymer with double bond in the chain. In that case both configurations cis and trans are equally possible. 

The bicyclic compound decahydronaphthalene, or bicyclo[4.4.0]decane, has two fused six-mem-bered rings. It exists in cis and trans forms (see Fig. 1.10), as determined by the configurations at the bridgehead carbon atoms. Both cis- and rran -decahydronaphthaiene can be constructed with two chair conformations. 

Configurations around any double bond give rise to cis and trans stereoisomerism. 

Maleic and fiimaric acids have physical properties that differ due to the cis and trans configurations about the double bond. Aqueous dissociation constants and solubiUties of the two acids show variations attributable to geometric isomer effects. X-ray diffraction results for maleic acid (16) reveal an intramolecular hydrogen bond that accounts for both the ease of removal of the first carboxyl proton and the smaller dissociation constant for maleic acid compared to fumaric acid. Maleic acid isomerizes to fumaric acid with a derived heat of isomerization of —22.7 kJ/mol (—5.43 kcal/mol) (10). The activation energy for the conversion of maleic to fumaric acid is 66.1 kJ/mol (15.8 kcal/mol) (24). 

Since the olefmic CC double bond is trisubstituted, the relative configuration cannot be determined on the basis of the cis and trans couplings of vicinal alkene protons in the H NMR spectrum. What is the relative configuration given the C NMR spectra 19 ... 

The decalin (bicyclo[4.4.0]decane) ring system provides another important system for study of conformational effects in cyclohexane rings. Equilibration of the cis and trans isomers reveals that the trans isomer is favored by about 2.8 kcal/mol. Note that this represents a change in configuration, not conformation. The energy difference can be analyzed by noting that the cis isomer has three more gauche butane interactions that are... 

NH2OH can exist as 2 configurational isomers (cis and trans) and in numerous intermediate gauche conformations as shown in Fig. 11.7. In the crystalline form, H bonding appears to favour packing in the trans conformation. The N-O distance is 147 pm consistent with its formulation as a single bond. Above room temperature the compound decomposes (sometimes explosively) by internal oxidation-reduction reactions into a complex mixture of N2, NH3, N2O and H2O. Aqueous solutions are much more stable, particularly acid solutions in which the compound... 

All the asymmetric thiirane oxides which have been obtained through this procedure are mixtures of the two possible cis- and trans- syn- and anti-) configurations, but the antiisomer predominates. 

If the carbanion has even a short lifetime, 6 and 7 will assume the most favorable conformation before the attack of W. This is of course the same for both, and when W attacks, the same product will result from each. This will be one of two possible diastereomers, so the reaction will be stereoselective but since the cis and trans isomers do not give rise to different isomers, it will not be stereospecific. Unfortunately, this prediction has not been tested on open-chain alkenes. Except for Michael-type substrates, the stereochemistry of nucleophilic addition to double bonds has been studied only in cyclic systems, where only the cis isomer exists. In these cases, the reaction has been shown to be stereoselective with syn addition reported in some cases and anti addition in others." When the reaction is performed on a Michael-type substrate, C=C—Z, the hydrogen does not arrive at the carbon directly but only through a tautomeric equilibrium. The product naturally assumes the most thermodynamically stable configuration, without relation to the direction of original attack of Y. In one such case (the addition of EtOD and of Me3CSD to tra -MeCH=CHCOOEt) predominant anti addition was found there is evidence that the stereoselectivity here results from the final protonation of the enolate, and not from the initial attack. For obvious reasons, additions to triple bonds cannot be stereospecific. As with electrophilic additions, nucleophilic additions to triple bonds are usually stereoselective and anti, though syn addition and nonstereoselective addition have also been reported. 

Photochemical [2h-2] cycloadditions of olefins occur with retention of configuration according to the Woodward-Hoffmarm rule [6,7], These are excited-state reactions in the delocalization band of the mechanistic spectrum. A striking example of the symmetry-allowed reaction was observed when the neat cis- and tran -butenes were irradiated (delocahzation band in Scheme 3) [8],... 

This dry ozonation procedure is a general method for hydrox-ylation of tertiary carbon atoms in saturated compounds (Table 1). The substitution reaction occurs with predominant retention of configuration. Thus cis-decalin gives the cis-l-decalol, whereas cis- and frans-l,4-dimethylcyclohexane afford cis- and trans-1,4-dimethylcyclohexanol, respectively. The amount of epimeric alcohol formed in these ozonation reactions is usually less than 1%. The tertiary alcohols may be further oxidized to diols by repeating the ozonation however, the yields in these reactions are poorer. For instance, 1-adamantanol is oxidized to 1,3-adamantane-diol in 43% yield. Secondary alcohols are converted to the corresponding ketone. This method has been employed for the hydroxylation of tertiary positions in saturated acetates and bromides. 

Duong and Gaudemer studied the alkylation of (presumably) [Co -(DMG)2X], where X is pyridine, aniline, or water, by the cis and trans isomers of )S-bromostyrene (PhCH=CHBr) and the methyl ester of )3-chloroacrylic acid (CHCl=CHCOOMe) in 50% aqueous methanol, and found that the configuration of the double bond remained unchanged, i.e., the halogen had simply been replaced by cobalt. They suggested that the reaction involved the addition of cobalt, followed by the elimination of the halide ion (apparently without rotation around the C—C bond), i.e.. 

By modification of the elegant method of preparation of optically active sulfinates previously reported by Mikolajczyk and coworkers , an efficient stereospecific method for the conversion of readily available optically active sulfinamides to optically active sulfinates of inverted configuration at the sulfinyl function, has been recently reported by Hiroi and coworkers . The same authors subsequently reported the thermal rearrangement of several optically active cis- and trans-y-substituted allylic p-toluenesulfinates to optically active chiral sulfones with high stereoselectivity. For example, trans and cis (S)-( — )-crotyl p-toluenesulfinates rearranged to optically active (S)-(-l-)- and (R)-( — )-a-methylallyl p-tolyl sulfone, respectively (equation 19). 

With two y,8 double bonds, two a,/3 double bonds, and the possibilities of cis and trans ring fusions with syn and anti configurations, 20 isomeric dimers are possible. Surprisingly, only one product is formed in a head-to-tail fashion. The sole product of the irradiation of the 3,5-diene-7-ketosteroid (76), however, is the head-to-head dimer. The specificity and mode of addition arise presumably through the effect of the specific environment of the chromaphore. The dimerization of (75) is believed to involve the addition of the a,fi double bond of a photoexcited molecule to the less hindered y,8 double bond of a ground state molecule. The photocondensation of (76) with cyclopentene, in which steric hindrance should not be a controlling factor, was found to yield a cyclobutane product involving the a,/ bond of the steroid in contrast to dimerization across the y,8 bond. 

The hydrogenation of 4-alkyl substituted anilines results in the production to two possible isomeric forms, cis and trans, and both of these isomers have two possible conformations in the chair configuration of the cyclohexyl ring. However experimentally it has been found that one cis and one trans conformer dominate. The dominant isomers are shown in Figure 1. 

Cleavage b in Scheme 4.4 Inversion of configuration The cis isomer reacts faster than trans Occurs on Pt and Pd Cleavage a in Scheme 4.4 Retention of configuration Both cis and trans react with similar rates Occurs on Ni and Cu... 

Since vinyl anions generally retain configuration 39> while isomeric vinyl radicals rapidly interconvert 40) these results constitute evidence that reductions of alkyl iodides do proceed via radical intermediates. Isomerization of stereoisomeric vinyl anions is ruled out by the lack of effect of phenol on the stereochemistry of the products (Scheme III). Since cis and trans-3-hexene are formed in differing proportions from the two halides, it may be concluded that the stereoisomeric vinyl radicals are being intercepted by electron trans-... 

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