Matrix isolation infrared and ab initio study of the 1 : 1 complexes of cyclopentadiene with nitrogen and oxygen bases: C-H center dot center dot center dot(NO) hydrogen bonding involving an sp(3)-hbridized carbon

Hydrogen-bonded complexes of cyclopentadiene with the strong bases ammonia, trimethylamine, and dimethyl ether have been isolated and characterized fo r the first time in argon matrices at 16. K. Coordination of the acidic alk yl hydrogen to the electron donor was evidenced by distinct red shifts of t he CH2 stretching modes of cyclopentadiene in the infrared spectrum. An add itional NH . . . pi interaction was evidenced by the red shift of an olefin ic C-H stretching mode. Ab initio calculations yield a complex with NH3 loc ated above the ring, oriented by both of these hydrogen-bonding interaction s. The calculated interaction energy of the complex is 2.40 kcal/mol, with the energy being divided equally between these two interactions. This study represents the first example of an sp(3)-hybridized carbon on a hydrocarbo n taking part in a C-H . . .N(O) hydrogen bond.