Abstract
The authors presented the tables for chemical shifts of alkane, alkene and alkyne carbons.
C-13 NMR chemical shifts were greatly influenced by neighbouring functions, and it was found convenient to arrange the tables so as to collect chemical shifts of carbons which accompanied the same sorts of neighbouring groups, i. e. chemical shifts of C-13 in X-13C-Y chemical structure were arraied in conjunction with X and Y functions. This method of classification was advantageous in that the difference of chemical shift of a certain type of carbon such as sp3, sp2 or sp which followed only different function might be estimated.
The references cited for the tabulation of C-13 NMR chemical shifts were the same as in the previous papers.
The numbers of chemical shifts collected here were: alkane; ca. 800, alkene; ca. 200 and alkyne; ca. 30.
Fig. 1 in the paper showed the chemical shift ranges of methyls. They distributed from 130 to 200 ppm from CS2. Metal methylate, silicate, nitrile and alkyne adjacent carbons resonated at the highest field. The terminal methyl of hydrocarbons had such a tendency as the nucleus which followed methylene was at the highest field and the carbons followed by methine and quaternary carbons lowly shifted nearly at intervals of 10 ppm respectively. Methyls which leaded sp2 carbons resonated in the range of 160 to 180 ppm regardless of olefinic or aromatic carbons. Ether and alcohol methyls were at the lowest field ranging from 130 to 145 ppm.
Fig. 2 was for methylene carbons. Generally speaking, the chemical shifts dropped about 10 ppm in comparison with methyls when the neighbouring functions were the same, and this relation was also observed between methylene carbons and that of methine and quaternary.
Fig. 4 was for olefinic carbons. They appeared in the range of 40 to 90 ppm except allene carbons. The terminal and centered carbons of allene resonated at higher than 100 and lower than -6 ppm respectively. There occured a case that the chemical shift ranged rather widely as shown in the line of unsaturated acids, it must be caused by steric effects of substituents.
Fig. 5 was for alkynes.
An application of the figures for the analysis of a C-13 NMR spectrum was presented.
