Conformational potential function for cyclopropylamine and a vibrational assignment for cyclopropylamine-d2

Abstract

The conformational potential function for cyclopropylamine has been calculated from far-infrared spectra of gaseous cyclopropylamine-d0 and cyclopropylamine-d2. The spectrum of the -d2 molecule is much simpler to interpret because the substate splitting for the gauche conformer is smaller. The asymmetric potential function has been calculated with an enthalpy difference of 699 cm"1 (2.00 kcal/mol) between the more stable trans and the high-energy gauche conformers for the -d2 molecule; the trans/gauche barrier is similar to that of isopropylamine. Quantities determined in this study are compared with those calculated from the theoretical study of the structure and bonding of this molecule. Mid-infrared (3200-500 cm'1) spectra of the vapor and Raman spectra (3400-10 cm"1) of fluid cyclopropylamine-d2 have also been recorded and a vibrational assignment is proposed. These results are compared with the similar data for the -d0 molecule.

Probing theEndo/ExoIsomeric Variants of a Binary Complex of Cyclopropylamine withp-Fluorophenol by LIF Spectroscopy: A Comparative Study with Ammonia Complex

“…The overall shape of the potential energy curve obtained here resembles the same of the CPA monomer quite well. The calculated absolute energy difference between the isomers is about 1.9 kcal/mol, which recalls the fact that the conformational energy difference between the trans and gauche isomers of bare CPA is almost alike (2.0 kcal/mol). , …”

“…The calculated absolute energy difference between the isomers is about 1.9 kcal/mol, which recalls the fact that the conformational energy difference between the trans and gauche isomers of bare CPA is almost alike (2.0 kcal/ mol). 34,35 Scan results also reveal that the exo (B) to endo (A) conversion barrier of the complex is about 1.6 kcal/mol, which is similar to the gauche to trans conversion barrier (1.8 kcal/ mol) in the free CPA molecule for calculation at the CAM-B3LYP/6-311++G(2d,2p) level (Figure S2). Therefore, the population distribution of the conformers for the present complex is expected to be more or less similar to that of the free CPA molecule.…”

“…In the case of the bare CPA molecule, a trans conformer where the lone pair electron orbital of nitrogen is oriented cis to the terminal C–C bond of the cyclopropane ring has been suggested to be preferred in earlier studies. − This conformer is predominantly stabilized by the interorbital interactions involving the lone pair electron orbital of nitrogen and orbitals of the cyclopropane ring. In the present study, a binary complex between CPA and one of the simplest substituted phenols, p -fluorophenol ( p FP), has been used as the target system (Scheme ).…”

Conformational preferences and basicities of monofluorinated cyclopropyl amines in comparison to cyclopropylamine and 2-fluoroethylamine

“…† The conformational potential function of cyclopropylamine (1) was estimated experimentally from the measured infrared and Raman spectra. 28,29 The lowest energy structure was found to correspond to the symmetric s-trans conformer 1a and the DH of the gauche conformer 1b/1c was estimated as 2 kcal mol -1 28 or 1.69 kcal mol -1 , respectively. 29 In the following, s-trans means that the protons at nitrogen point away from the cis-protons at carbon relative to nitrogen and s-cis means that the protons at nitrogen point towards the cis-protons at carbon.…”

“…26, 27 Adding zero-point vibrational energies and thermal corrections gives DH 298 of 2.02 kcal mol -1 (SCS-MP2) which is in excellent agreement with the experimental value of 2.00 kcal mol -1 from ref. 28.…”