The influence of substituents on the~(13)C-NMR chemical shifts of meta-and/para-substituted phenylacetylenes

摘要

The introduction of substituents on to the phenyl ring of phenylacetylene has been investigated to determine their effects on the~(13)C-NMR chemical shift of the terminal acetylenic carbon atom.Both electron donating and electron withdrawing substituents were studied.It has been demonstrated that three different effects,direct resonance,secondary resonance and n polarisation,cause changes in chemical shift when substituents are introduced on to the benzene ring of such molecules.The impact of these effects was also found to be dependent upon the position of the substituent in relation to the acetylene group.