Intrinsic carbon‐13 NMR solvent shifts in hydrocarbons. Relevance of long range substituent parameters

Abstract

Abstract-Carbon-13 NMR chemical shifts have been measured in a number of binary mixtures of normal alkanes. Intrinsic solvent substituent effects in alkanes is discussed. A comparison is made between solvent effects and thermally induced chemical shift Hydrocarbon TABLE 1 . CHEMICAL SHIFTS VERSUS E X T~K N A L TMS IN SOMF >FAT LINEAR ALKANES AND I N SOME BINARY MIXTURES, E X T R A P O L A~~D TOshifts are deduced from the shifts and the relevance of some small INFINITE DILUTION differences in alkane3.c,

Additional insights from very‐high‐resolution 13C NMR spectra of long‐chain n‐alkanes

“…Unfortunately, none of these spectra are shown in these reports for 13 , 16 , 18 , and 20 . 13 C chemical shifts to two decimal places are reported for 13 , 16 , and 18 , but no 13 C chemical shifts are reported for 20 in CDCl 3 (only that the signals for C‐7 through C‐10 are not resolved at 100.56 MHz 13 C) . One report for 16 in CDCl 3 showed partial resolution of the signal for C‐6 from the completely overlapped signals for C‐7 and C‐8 at just 5.87 T (62.88 MHz 13 C) .…”

“…Since then, others have reported six resolved signals for n ‐undecane in CDCl 3 and for n ‐dodecane ( n ‐C 12 H 26 , 12 ) neat or in CDCl 3 , C 6 D 6 , C 6 D 5 CD 3 , or C 6 H 5 Cl . For longer n ‐alkanes, there are reports of six of the seven possible 13 C signals for n ‐tridecane ( 13 ) in CDCl 3 ; six of the eight possible 13 C signals for n ‐hexadecane ( n ‐C 16 H 34 , 16 ) in the neat liquid or in CDCl 3 ; six of the nine possible 13 C signals for n ‐octadecane ( n ‐C 18 H 38 , 18 ) in CDCl 3 , C 6 D 6 , C 6 D 5 CD 3 , or C 6 H 5 Cl; and seven of the ten possible 13 C signals for n ‐eicosane ( n ‐C 20 H 42 , 20 ) in CDCl 3 . Unfortunately, none of these spectra are shown in these reports for 13 , 16 , 18 , and 20 .…”

“…For longer n ‐alkanes, there are reports of six of the seven possible 13 C signals for n ‐tridecane ( 13 ) in CDCl 3 ; six of the eight possible 13 C signals for n ‐hexadecane ( n ‐C 16 H 34 , 16 ) in the neat liquid or in CDCl 3 ; six of the nine possible 13 C signals for n ‐octadecane ( n ‐C 18 H 38 , 18 ) in CDCl 3 , C 6 D 6 , C 6 D 5 CD 3 , or C 6 H 5 Cl; and seven of the ten possible 13 C signals for n ‐eicosane ( n ‐C 20 H 42 , 20 ) in CDCl 3 . Unfortunately, none of these spectra are shown in these reports for 13 , 16 , 18 , and 20 . 13 C chemical shifts to two decimal places are reported for 13 , 16 , and 18 , but no 13 C chemical shifts are reported for 20 in CDCl 3 (only that the signals for C‐7 through C‐10 are not resolved at 100.56 MHz 13 C) .…”