Electronic Transition in Formaldehyde

Electronic Transition Expected in HCHO

Electronic Transition Expected in Formaldehyde

In formaldehyde, each C-H bond arises by the linear overlap of sp² orbital of carbon and 1s orbital of H atoms. Hence, C-H bonds are sigma bonds. A sigma bond between carbon and oxygen atoms arises by the linear overlap of sp² orbital of carbon atom and sp orbotal of oxygen atoms and a ℼ-bond by the lateral overlap of 2p_x and 2p_y orbitals-

The oxygen atom has two lone pairs of electrons- one 2p_y orbital and other in sp orbital. The lone pair present in 2p_y orbital can coordinate due to greater p-character because the dumb bell p-orbital is more extended in space than the spherical s-orbital.
From the molecular orbital diagram, it is clear that forma;dehyde shows two transitions in uv-vis spectra. π → π* at 185nm and n → π* at 270nm. The latter has two lower intensity than the former due to forbidden nature.

Electronic Transition Expected in Ethene

Electronic Transition Expected in Butadiene

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