Vibrational spectra of N-2'-methyl-propyliden-propan-2-amine : conformational analysis and influence of the nitrogen hybridization

Abstract Infrared and Raman spectra of the (CH 3 ) 2 C 2′ HC 1′ HNCH(CH 3 ) 2 aldimine (NPP) and of two deuterated derivatives at C 1′ and C 2′ in the liquid, solid and solution phases have been recorded and assigned between 4000 and 130 cm −1 . NPP adopts the E configuration and two conformers at the C sp 2 and N sides are in equilibrium. Some vibrational modes are specifically assigned to the anticlinal ( ac ) or synperiplanar ( sp ) conformers at the C sp 2 side. The ac (C sp 2 ) form is dominant in the pure liquid whilst the sp (C sp 2 ) form is favoured in the solid and in chloroform. The vibrational dynamics of the isopropyl group on both sides of the CN bond are partially similar to that of the (CH 3 ) 2 CHCHO aldehyde on the one hand and of the (CH 3 ) 2 CHNH 2 amine on the other hand. When moving from the amine to the corresponding aldimine, changes about νNC and wCC 2 modes (at the N side) are related to electronic and geometrical effects as a consequence of the nitrogen hybridization change from sp 3 to sp 2 .