Conformation trans-gauche

Other Polysilylenes. The symmetrically substituted poly(di-n-tetra-decylsilylene) is reported to have a TGTG trans-gauche-trans-gauche ) conformation, and a bathochromic shift is observed in the UV spectrum at 54 °G with Xjnax shifting from 322 to 350 nm (35). The structures of many polysilylenes may be more complicated than what have been discussed thus far. As an example, the DSG data for PMHS are shown in Figure 24, The figure shows that Tg (glass transition temperature) is 220 K and that two... 

The bonding in vinylcyclopropane (3) is such that an s-trans-gauche conformational equilibrium exists to allow for maximum orbital overlap of the asymmetric component of cyclopropane orbitals with the IT- or 7T -orbitals of the ethylene unit, as shown in (3a). From thermochemical stuches it appears that conjugation of an alkene with cyclopropane stabilizes the system by 1.2 kcal mol". The conformational equilibrium for vinylcyclopropane was shown to consist of an s-trans minimum (3b) and two gauche conformers that are equ in energy and destabilized by 1.43 kcal mol with respect to the s-trans conformation. The barrier to interconversion has been determined to be 3.92 kcal mol . ... 

The vinylcyclopropane chromophore takes an exceptional position among the compounds in which a double bonded group is linked to the cyclopropane ring. In the parent molecule, vinylcyclopropane (127), there is a s-trans-gauche conformational equilibrium whereas in all other related double bonded compounds (acids, aldehydes, etc.) s-trans and s-cis conformers are preferred... 

With FTIR analysis, we determined the correct window in X-ray illumination time (for our structures, max. 20 min). Under X-ray irradiation, the copolymer is slowly degenerated fi om the p-phase or a)X-trans conformation into the trans-gauche conformation. 

This corresponds to the gauche+-trans-trans-gauche+ (and gauche--trans-trans-gauche ) conformation, and has a fiber repeat of 16.24X. The second and third conformations are both compatible with the observed monomer repeat. The remaining minima are for all-gauche options, of which the most extended conformation has a repeat of 15.31, significantly shorter than the observed value. 

Figure 7. Predicted conformation for poly(MDI-EDO) (12). The ethylene glycol unit has the gauche -trans-gauche conformation the fiber repeat is 15.0 A.

Recently Hagen and Hedberg studied several oxalyl halides by electron diffraction. Their data demonstrated the presence of trans-gauche conformers rather than trans-cis conformers. Similar questions regarding orientation about the C-C single bond in the conjugated molecules, biphenyl and the haloderivatives have been extensively studied by Bastiansen and co-workers. ... 

The kinked-chain structure is based on a gauche(- -)-trans-gauche(—)conformation that leaves the chains parallel and causes a contraction in the chain direction by c/2 with expansions in the a and b directions of about 0.2 nm. The latter may be recovered over several bond-lengths by elastic deformations of the defect region... 

Complexes of MXs with dinitriles CN(CH2) CN ( = 1-4) have been prepared.Both [MXsL] and [MXsL ] have been isolated in the case of malonitrile, succinonitrile and glutaronitrile, whereas only [(MXs)2L] formed with adiponitrile. In the case of succinonitrile and glutaronitrile, trans conformers have been assigned to the 2 1 adducts, while a gauche conformation was assumed in 1 1 complexes the more stable gauche-trans-gauche conformation for adiponitrile was proposed in its 1 2 adducts. 

Scheme 2. a and 8 form with alternating trans-gauche conformation (J. H. Yen, 2006)... 

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