Configurational properties of ۱,۲-propadiene, ۱-ger ma-۱,۲-pr opadiene, ۱.۲-digerma-۱,۲-propadiene and ۱,۲,۳-trige rma-۱,۲-propadiene . A hybrid density func tional theory study and natural bond orbital interpretatio n

Cumm ulenes (H۲ CnH۲; n>۲) and the corresponding cummulenecarbenes (CnH۲; n>۲) p resent important reactio n intermedi ates in combustion fla mes,۱chemical vapor de position,۲ and in interstellar environments.۳Whereas all cu mmulenecarbenes hold a C۲ symmetry and depi ct ۱A۱ electr onic ground states, the situation for the cummulenes is mor e complex.۴ Here, mole cules havin g an even umber of carbon atom s belong t o the D۲h point group, whereas a n odd numb er of carbon atoms dictate an inherent D۲d sym metry.۵This correlates with ۱Ag and ۱A۱ electr onic ground states of the even a nd odd-nu mbered cum mulenes, respectively. The struct ures of the cummulene s also correlate with recent studies of ۱۳C nuclear ma gnetic resona nce (NMR) paramagnetic shieldin g constants. Due to their unique ele ctronic structure, cummulenes hold also important technical potential as elements for molecu lar machin es the cationic forms serve as mod els for molecular wire s.۶There is much published data about carbo ncummulen es, there is no sufficient information about their analo gs containing Ge atoms. For this purpose the ground and transition state structures of ۱,۲-propadiene(۱),۱-germa-۱,۲-propadiene(۲),۱,۲-digerma-۱,۲-propadiene(۳)and۱,۲,۳ -trigerma-۱, ۲ propadie ne(۴)have been optimized by density functio nal theory (DFT) based method, at B۳LYP/۶-۳۱G* level of theory, using the GAUSSIAN ۰۳ package of progr ams.۷The B۳LYP functional method combines Becke’s three-paramet er exchange function with the correlation function of Lee et al. Also, NBO (natural bond orbital) analysis was used to investigate the nature of the bonds in compoun ds ۱–۴.۸

کلیدواژه ها:

DFT ، NBO ، germa propadiene