NMR 13C NMR 17O NMR Conformational effects Substituent effects article 13C chemical shift measurement 13c chemical shifts 13c nmr 17O chemical shifts 1H chemical shifts 1J(C,H) 2-methylpropenes 5-X-salicylaldehydes Ab initio LORG study Aldehydes Alkyl formates Allylic couplings Antibonding orbitals Carbon monoxide Carbon-fluorine coupling Computational geometry Concentration (process) Conformations Conjugative interactions Continuum mechanics DFT-NBO; DFT-GIAO Dielectric materials Dual path transmission Fermi level