Knowledge Bank

The $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}U$ ($n\pi \ast$) $\leftarrow$ $So$ absorption spectra of benzaldehyde, benzaldehyde -1-d, -4-d, and -$d6$ were measured in the vapor state at $26\circ C$ using a White cell with a 40 m pathlength. The assignments of vibronic bands to particular normal modes have been made. The experimental results establish that $v11$ is by far the most active mode. The extent of the delocalization of the n- electrons into the benzene ring and the importance of the hydrogen modes in the $700-800cm-1$ region upon the vibronic intensification is discussed.