Lowering of Bohlmann band intensities in conformationally homogeneous 2,6-diarylpiperidines due to ring distortion

Abstract

<span style="font-size:14.0pt;mso-bidi-font-size:10.0pt; font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">The orientation of the lone pair of electrons on the nitrogen in 2,6- diarylpiperidin-4-ones and 2,6-diarylpiperidines has been studied employing the Bohlmann bands in the IR spectra. Increase in the number of alkyl substituents at C-3 and C-5 positions decreases the intensities of the Bohlmann bands indicating that the nitrogen lone pair is axial in these amines in the solid state and depending upon the number and bulkiness of the substituents at C-3 and C-5 the ring is twisted or flattened resulting in a decreased interaction between the lone pair and the antiperiplanar hydrogens. The flattening of the ring due to the introduction of alkyl substituents at C-3 and C-5 positions has also been derived from X-ray diffraction data.</span>