The Influence of Polytypic Structures on the Solid-state 13C NMR Spectra of n-Alkanes

Abstract

Two polytypes for the monoclinic (M011) modification of n-hexatriacontane (n-C36H74), single-layered structure Mon and double-layered structure Orth II, were studied by means of the solid-state CP/MAS 13C NMR spectroscopy. The terminal methyl carbon showed clear differences in the chemical shift as well as spin-lattice relaxation time (T1) between Mon and Orth II, in contrast to no marked difference for the other carbons.

13C Solid-State NMR Analysis of the Chemical Structure in Petroleum Coke during Idealized In Situ Combustion Conditions

“…This can provide more evidence on the state of hybrid orbitals, the induced and conjugated effects of substituent groups, and the stereoscopic structure of molecules to determine which are the main factors affecting the chemical shifts of carbon atoms. 25 , 26 …”

“…A saturated hydrocarbon carbon atom, olefin carbon atom, alkyne carbon atom, and carbonyl carbon atom have different chemical shift δ values due to the different shielding effects of carbon atoms in compounds in a different environment. This can provide more evidence on the state of hybrid orbitals, the induced and conjugated effects of substituent groups, and the stereoscopic structure of molecules to determine which are the main factors affecting the chemical shifts of carbon atoms. , …”

“…This can provide more evidence on the state of hybrid orbitals, the induced and conjugated effects of substituent groups, and the stereoscopic structure of molecules to determine which are the main factors affecting the chemical shifts of carbon atoms. 25,26 The carbonyl group does not have a corresponding signal in the 1 H NMR spectrum but does have a corresponding characteristic absorption peak in the 13 C NMR spectrum. 27 The π bond of CO in carbonyl compounds is easy to polarize so that the density of the electron cloud on the carbonyl carbon atom becomes smaller, and the chemical shift value tends to be lower than that of olefin, which is generally in the range of 160−220 ppm.…”