Theoretical studies of NMR chemical shifts and vibrational frequencies in lambda(3)-phosphaalkynes P C-R

A range of lambda(3)-phosphaalkynes P=C-R (R = F, Cl, O-, OLi, OH, OSiMe3, S-, SLi, SH, Me, SiMe3, H)(1) has been geometry-optimized at the HF, MP2, a nd CCSD(T) level of theory. Vibrational frequencies as well as P-31 and C-1 3 NMR chemical shifts were calculated and compared to experimental values o f the large variety of lambda(3)- phosphaalkynes prepared over several year s via differing synthetic routes. With a few obvious exceptions, a good agr eement of calculated and experimental parameters was found. This also opens up the possibility to make predictions on spectroscopic data of compounds not yet synthesized or fully characterized, e.g., PCOSiMe3 and PCSH. The bo nding situation especially of the negatively charged species P=C-O- and P=C -S- was studied via NBO analyses to determine the degree of phosphaalkyne a nd heterocumulene contributions to the mesomeric anions.