¹³C NMR studies of the conformation of cyclic paraffins, n‐paraffins and polyethylene in solution

Abstract

High-resolution l 3 C NMR spectra of cyclic paraffins, n-paraffins and polyethylene were measured in 1,2,4trichlorobenzene solution, and the results were compared with the solid state 13C high resolution NMR data measured previously. It is proposed that in cyclic paraffins up to C&, the conformation in the solid state is retained even in solution, all the methylene carbons within the cyclic paraffin exhibiting identical gauche-trans population with fast transition between the conformers in the ring plane, whereas in cyclic paraffins of larger carbon number, the conformation in the solid state is not retained in solution, the gauche-trans populations being different in this case. The conformation of n-paraffins and polyethylene is also discussed.

Solid-state13C NMR Study on Order → Disorder Phase Transition in Oleic Acid

“…It is well-known that the chemical shift of carbon atom is influenced by the change in the electronic structure from the conformational change. In particular, the γ gauche effect , and vicinal gauche effect , are studied by both experiments and theoretical calcultions. − According to these studies, when the conformation of a C−C bond changes from trans to gauche, the peaks due to the carbons in proximity to the C−C bond show upfield shifts.…”

Conformation and dynamic aspects of poly(.gamma.-n-octadecyl L-glutamate) in the solid state and liquid-crystalline state as studied by variable-temperature carbon-13 CP/MAS NMR spectroscopy

“…Recently, Watanabe et al 1 have reported that in a series of -helical poly(L-glutamates) with n-alkyl side chains of various lengths (n (number of carbon atoms in the alkyl group) = [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], n-alkyl side chains longer than = 10 form a crystalline phase composed of paraffin-like crystallites together with the -helical main chain packing into a characteristic layer structure. The polymers form thermotropic cholesteric liquid crystals by the melting of the side-chain crystallites.…”

Pyrolysis of Alkanes: A Computational Approach

“…Since the termination steps are the combinations of reactive intermediates and unproductive steps, they are neglected in the reaction network for simplicity. To analyze the kinetics of propane pyrolysis, these steps were modeled at a moderate temperature of 673 K, and in vacuum, the latter reflects the physical environment inside the delayed coker unit. , The n -alkanes are in all-trans zigzag conformation since this is the most stable conformation for unbranched alkanes according to X-ray studies − and our DFT calculations. The results are summarized in Table in terms of activation energy ( E a ), calculated using eq , and compared to the available experimental data for each reaction step.…”