Cis-lrans isomers

S)-11 yield 39% (mixture of cis/trans-isomers) (25)12 yield 20.5 % (mixture of cis/lrans-isomers)... 

Mefarhodopsin II is then recycled back into rhodopsin by multi t st p sequence involving cleavage to all lran reiinft1 and cis-tntmi isom erlzatton back to ll-cis-retinal. 

Monoalkyl- and monoaryldiazoalkanes yield, on treatment with sulfur dioxide, cis/lrans mixtures of episulfones. However, in the reaction of disubstituted diazoalkanes with sulfur dioxide mainly trans-isomers are formed112-115,... 

Although t.ho cis-lrans intcrconversion of alkene isomers does not occu. spontaneously, it can often Ire brought about by treating tire alkene with a strong acid catalyst. If we interconvert ds-2-butene with frc7//.s-2-butene and allow them to reach equilibrium, we find that they aren t of equal stability. I he trans isomer is more stable than the cis isomer by 2.8 kj/mol (0.66 kcal/mol) at room temperature, leading ro a 76 24 ratio. 

Hashimoto H, Koyama Y, Ichimura K and Kobayashi T (1989) Time-resolved absorption spectroscopy of the triplet state produced from the all-trans, 1-cis, 9-cis, 13-cis, and 15-dv isomers of /3-caroteiie. Chem Phys Lett 162 517-522 Hashimoto H, Koyama Y, Hirata Y and MalagaN (1991) S and TI species of j3-car0tene generated by direct photoexcitation from the all-lrans, 9-cis, 13-ds, and 15-dv isomers as revealed by picosecond transient absorption and transient Raman spectroscopies. J Phys Chem 95 3072-3076 Hashimoto H, Miki Y, Kuki M, Shimamura T, Utsumi H and Koyama Y (1993) Isolation by high-pressure liquid chromatography of the cis-trans isomers of )3-apo-8 -carotenal. Determination of their So-state configurations by NMR spectroscopy and prediction of their S - and Ti-state configurations by transient Raman spectroscopy. J Am Chem Soc 115 9216-9225... 

The anti-diabetic effect of CLA may depend on both species and types of isomer. Rumenic acid seemed to be inactive (Martin Valeille, 2002), but the role of Irans-10,cis-12 isomer is controversial some studies verified decreasing glucose levels and increased insulin sensitivity with increased intake of lrans-10,cis-l2 CLA (see the review by Khanal, 2004), while others reported opposite effects - that is, the promotion of insnlin resistance (Khanal, 2004 Moloney, Yeow, Mullen, Nolan, Roche, 2004 Wang Jones, 2004). 

In summary, all the experiments expressly selected to check the theoretical description provided fairly clear evidence in favour of both the basic electronic model proposed for the BMPC photoisomerization (involving a TICT-like state) and the essential characteristics of the intramolecular S, and S, potential surfaces as derived from CS INDO Cl calculations. Now, combining the results of the present investigation with those of previous studies [24,25] we are in a position to fix the following points about the mechanism and dynamics of BMPC excited-state relaxation 1)photoexcitation (So-Si)of the stable tram) form results in the formation of the 34 cis planar isomer, as well as recovery of the tram one, through a perpendicular CT-like S] minimum of intramolecular origin, 2) a small intramolecular barrier (1.-1.2 kcal mol ) is interposed between the secondary tram and the absolute perp minima, 3) the thermal back 3-4 ds- lrans isomerization requires travelling over a substantial intramolecular barrier (=18 kcal moM) at the perp eonformation, 4) solvent polarity effects come into play primarily around the perp conformation, due to localization of the... 

Solution 19 Cis-lrans stereoisomers are possible only for 3,4-dimethylcyclohexene. The ring size and geometry of the double bond prohibit a trans configuration of the double bond. Two configurational isomers (they are enantiomers) are possible for 2,3-dimethylcyclohexene. 

Thermolysis of 2,7-dihydrothiepine dioxides gives trienes and sulphur dioxide. The c >2,7-dimethyl compound is converted into rrans,ciXd5 octatriene (Equation 6.131) while the trans-isomer gives the trans,cis,lrans-oct tnene. The stereospecificity is greater than 97 per cent and the results clearly indi-... 

Problem 9.41 Explain why (a) a carbene is formed by dehydrohalogenation of CHCI, but not from methyl, ethyl, or -propyl chlorides b) m-1,3- and /rawj-l,4-di-/ert-butylcyclohexane exist in chair conformations, but their geometric isomers, lrans-1,3- and cis-1,4-, do not. <... 

Octahydro- (we have used this nomenclature throughout) or perhydrobenzo[c]thiophene (35) exists as the cis and trans isomers and is more commonly named 2-thiahydrindane or 8-thiabicyclo-[4.3.0]nonane. Each stereoisomer may be prepared by treating the corresponding isomer of l,2-di(bromomethyl)cyclohexane with sodium sulfide (details of the products are given in Table IV).45 Cyclization of the cis isomer may be effected partially with thiourea via the formation of cis-hexahydro-o-xylylenebis(isothiouronium bromide) with sodium disulfide it gives a mixture of cis-octahydro-benzo[c]thiophene and cis-2,3-dithiadecalin.46 Optically pure ( —)-(8 R,9I )-lran -octahydrobenzo[c]thiophene has been prepared from (+ )-dicarboxylic acid via reduction of the diacid to the diol, tosylation, and ring closure of the bistosylate with sodium sulfide.47... 

The trans and cis isomers of l-bromo-4-rert-butylcyclohexane can be taken as models to estimate the chemical shift of the proton of the CHBr group when it is axial and equatorial, respectively, in the two chair conformations of bromocyclohexane. An axial proton is more shielded (5 3.81 ppm for lran -l-bromo-4-ferf-butylcyclohexane) than an equatorial one (S 4.62 ppm for cis- -htomo-4-tert-buty Icy clohexane). 

The alkaline hydrolysis of ethyl c/s-2-hydroxycyclopentanecarboxy-late is 1.8 to 11 times faster than that of ethyl cyclopen tanecarboxy late but this rate difference probably does not arise from intramolecular catalysis since the trans-isomer for which such catalysis is unlikely reacts even faster. The solvent dependence of the rates of both the cis- and lrans-2-hydroxy esters in aqueous dioxan is much smaller than that for ethyl cyclopentane-2-carboxylate and this was tentatively attributed to solvent sorting [53]. 

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