Knowledge Bank

Benzyl compounds $(C6H5C\alpha H2X)$, generally fall into two conformational classes. With $X=CH3,C2H5,F$, or Cl, the $C-C-C\alpha -X$ dihedral angle is $90\circ$; with $X=CN$ and CCH, the dihedral angle is $0\circ$; however, benzyl alcohol $(C6H5CH2OH)$ and benzyl amine $(C6H5CH2NH2)$ have asymmetric structures. Two conformers of benzyl amine have been $observed,a$ one with a dihedral angle approximately $50\circ$ and a higher energy form with dihedral angle $90\circ$. Benzyl alcohol has a single asymmetric conformation with dihedral, $C-C-C\alpha -O$ about $60\circ$ . The microwave rotational spectrum displays tunneling doublets for all transitions indicating a low barrier path between two of the four equivalent energy minima. These splittings are significantly smaller in the $C6H5CH2OD$ spectrum. The rotational spectrum of sec-phenethanol, $(C6H5C\alpha H(C\beta H3)OH)$, displays a single conformation with $C-C-C\alpha -C\beta$ dihedral angle approximately $90\circ$ and the $C-C-C\alpha -O$ dihedral angle approximately $30\circ$, and no tunneling split transitions, ab initio calculations on sec-phenethanol and benzyl alcohol will also be discussed.