Isomerization, cis and trans

Bushnell and co-workers [117] employed extensive molecular modelling to understand the nature of cis and trans isomerism in tetrahedral p-phenylene vinylene oligomers, and to aid the interpretation of time of flight mass spectrometry and ion mobility studies. Molecules such as T4R, shown in Figure 18, with four equivalent arms can be used to control the crystallinity in thin films. The authors reported the observation of a species in the mass spectrum resulting from the loss of an arm from the central carbon. This species will be referred to as P4R. 

Derivatives 30 (R OH, R2 = iV-acetyl-indol-3-yl-(CH2)2 and (R = OEt, R2 = Ph-(CH2) (n — 2, 3)) were transformed into intramolecular Friedel-Crafts type reactions involving A-acyliminium cation intermediates into the cis-and trans-isomeric mixtures of the corresponding fused derivatives on treatment with strong acid <2000TL2745, 2001JOC5731>. 

A rather complex reactivity towards the cyclopropenone system is exhibited by N-nucleophiles. Thus, ammonia reacts with diphenyl cyclopropenone to yield either the enamino aldehyde 323222> or a mixture of the cis and trans isomeric diphenyl azetidinones 522223 depending on the reaction conditions these products result from primary addition of the nucleophile at C,(2 ... 

The chemist s knowledge of molecular geometry extends beyond typical values of bond distances. He will also be able to predict many bond angles fairly accurately. This is equivalent to specifying a 1-3 nonbonded interatomic distance. The chemist s sketch portrays cis and trans isomerization, syn and anti, and gauche conformations which specify either torsion angles, or indirectly, a 1-4 nonbonded distance. 

Trans-unsaturated fatty acid from its CIS- and trans-isomeric mixture Na-ZSM-5 [182]... 

The chemical shifts of a range of cis and trans isomeric pairs of 2-alkoxytetrahydropyrans (73) and (74) show a consistent upheld shift of the three carbon atoms attached to oxygen in the axial isomers. The effect is greatest at C-6 and smallest at the alkoxy carbon atom (81JOC4948). 

Ab initio MO calculations at the MP2(FC)/6-31G level of theory gave estimates of the activation barrier of 1 -methylcyclobutyl cation to the a-methylcyclopropylcarbinyl cation of about 20.0 kcal mol1. At MP2/6-31G + ZPE, the trans-isomer is 2 kcal mol 1 more stable than the cw-isomer, whereas the bent 1-methylcyclobutyl cation 9 is less stable than the trans-1 -methylcyclopropylcarbinyl cation 18 by 0.8 kcal mol"1 (vide supra). The MP2/6-31G optimized bond lengths (in A) for the cis and trans isomeric cations are as shown ... 

Given the name or abbreviated structure of an unsaturated compound, tell whether it can exist in cis and trans isomeric forms and, if so, how many. Draw them. 

Usually, a mixture of cis and trans isomeric thietane 1,1-dioxides is... 

Treating the 6-coordinate spheres in geometrical fashion, Werner demonstrated the possibilities for cis and trans isomerism. If the metal... 

In the planar complexes of metals showing the co-ordination number four there is a possibility of cis- and trans- isomerism ... 

With 6-co-ordinate octahedral complexes, geometrical isomerism is also possible. Cis- and trans- isomerism is found in an ion such as [CoCl2(NH3)J ... 

Bromide ion-mediated electrolyses of substituted cyclic sulfides result in cis and trans isomeric sulfoxides [76] ... 

An interesting ring contraction of the eight-membered heterocycle (168) furnished the spirocycle (169) in which the aromaticity is lost (equation 52). Unfortunately, the stereochemical integrity of the rearrangement product was not commented upon. Ylides are used for ring expansion reactions likewise. The cis and trans isomeric ylides (170) and (173) lead to the same rearrangement product (172 s 175) with a trans double bond (Scheme 22). This result can be rationalized on the assumption that in each of the transition states (171/174) the ester enolate is equatorial. 

The cis and trans isomeric mixtures of di-oxolane congeners bearing sulfur, phosphorus, or arsenic cationic heads (113-115)dis-play lower muscarinic effects than the corresponding nitrogen system (153). 

CAS 3724-65-0. CH3CH CHCOOH. Exists in cis and trans isomeric forms, the latter being the stable isomer used commercially. The cis form melts at 15C and is sometimes called isocrotonic acid. 

Properties Exists in cis and trans isomeric forms, both colorless liquids. D 1.225 (10/4C), flash p 95F (35C) (OC). Insoluble in water soluble in acetone, toluene, octane. Bp cis 104C, trans 112C, refr index (20C) cis 1.469, trans 1.475. 

The sulfonation of low molecular weight model olefins was undertaken to determine the feasibility of this approach. Competitive sulfonations using acetyl sulfate were carried out on the model compounds below, representing the repeat structures of cis-l,4-polyisoprene (PIP), cw-l,4-polybutadiene (c-PBD), and trans-l,4-polybutadiene (Z-PBD), respectively. It was necessary to model both the cis and trans isomeric forms of 1,4-polybutadiene, since ttey have a nearly equal probability of occurrence when the anionic polymerization (Ii counterion) is conducted in a nonpolar hydrocarbon medium... 

The simplest unit is 1,4-isoprene, although there are two distinct cis and trans isomeric configurations of 1,4-polyisoprene. 

A third backbone index trans was defined by Equation 12.24, as the number of carbon-carbon double bonds along the chain backbone which are in a trans configuration divided by the number NBB of backbone atoms. If there is a mixture of cis and trans isomerization around the C=C bonds along the chain backbone, only the trans double bonds are counted. For example, all-trans polyisoprene has one trans C=C backbone bond per repeat unit with NBB=4, so that... 

Chatt has recalled elsewhere his work on the synthesis of complexes of plati-num(ii) and the implications for structure arising from their stereoisomerism and the use of techniques such as the measurement of dipole moments to distinguish cis and trans isomeric forms. The extensive synthetic studies from the Russian school led by Chernyaev revealed the directing influence of ligands bound to metals in... 

Aryl ketones are often used to effect cis and trans isomerization of olefins. Although this, in some cases, can be viewed as an energy transfer process where the ketone triplet transfers its energy to the olefin, which then isomerizes, the failure of noncarbonyl sensitizers of comparable triplet energy to isomerize the olefins suggests that a process other than energy transfer may be involved. Schenck and Steinmetz suggested that isomerization results from decomposition of a biradical carbonyl-olefin adduct similar to that involved in oxetane formation ... 

Figure 3. Chemical structures of various cis and trans isomeric forms of neonicotinoids.

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