Spectroscopic and Quantum Chemical Study of Cyclopropylmethylphosphine, a Candidate for Intramolecular Hydrogen Bonding

Abstract

The properties of the novel compound cyclopropylmethylphosphine (C3H5CH2PH2) have been investigated by means of Stark-modulation microwave spectroscopy and high-level quantum chemical calculations. Spectra attributable to the three conformers of the molecule with a synclinal arrangement of the H-C-C-P atoms were recorded and assigned. The experimental rotational constants obtained for these conformers were found to be in good agreement with those generated by ab initio geometry optimizations at the MP2/aug-cc-pVTZ level of theory. An estimate of the relative energies of the three conformers with observable spectra, by means of relative intensity measurements, compared favorably with the results of G3 energy calculations performed for the molecule. In addition to the observation of ground-state rotational spectra for three conformers, spectra belonging to a number of vibrationally excited states were also assigned with the aid of radio frequency microwave double-resonance experiments. A tentative assignment of these excited-state spectra was proposed by appealing to the results of density functional theory vibrational frequency calculations performed at the B3LYP/6-311++(3df,2pd) level. The energetically preferred conformer of the molecule allowed a close approach between a hydrogen atom belonging to the phosphino group and the edge of the cyclopropyl ring. The possibility of the formation of an intramolecular hydrogen bond to electron density associated with so-called banana bonds is discussed.

Microwave and Quantum Chemical Study of the Hydrazino Group as Proton Donor in Intramolecular Hydrogen Bonding of (2-Fluoroethyl)hydrazine (FCH2CH2NHNH2)

“…Much of our work has focused on weak proton donor groups. Recently, we reported gas-phase studies of alcohols, − carboxylic acids, thiols, − thiolcarboxylic acids, selenols, − amines, − amides, , and phosphines, − where the said groups are proton donors in internal H bonds with acceptors such as the fluorine atom, ,,, the chlorine atom, ,,, π-electrons of triple bonds, − ,,,, π-electrons of double bonds, ,,,, and Walsh pseudo-π electrons. ,, References of many of our earlier works are found in the cited literature as well as in reviews. − …”

“…Recently, we reported gas-phase studies of alcohols, 1−5 carboxylic acids, 6 thiols, 7−10 thiolcarboxylic acids, 11 selenols, 12−15 amines, 16−18 amides, 19,20 and phosphines, 21−24 where the said groups are proton donors in internal H bonds with acceptors such as the fluorine atom, 1,6,9,11 the chlorine atom, 17,19,23,24 π-electrons of triple bonds, [3][4][5]7,13,15,18 π-electrons of double bonds, 2,8,10,14,21 and Walsh 25 pseudo-π electrons. 12,20,22 References of many of our earlier works are found in the cited literature as well as in reviews. 26−29 No gas-phase studies of hydrazines (R−NHNH 2 ), where the hydrazino group (−NHNH 2 ) acts as a proton donor, appear to have been reported.…”

Microwave Spectrum, Conformational Composition, and Dipole Moment of (Fluoromethyl)cyclopropane (C3H5CH2F)

“…Conformational and structural studies of methylcyclopropane derivatives (C 3 H 5 CH 2 X) have received considerable attention in the past. Microwave (MW), infrared (IR), and Raman spectroscopic studies, often augmented by quantum chemical calculations, have been reported for a number of them including X = F, − Cl, ,− Br, ,,, I, , OH, SH, SeH, NH 2 , PH 2 , CH 3 , SiH 3 , − SiF 3 , ,, CN, , CCH, , and NC …”

“…The gauche effect should also favor the synclinal orientation, especially when X is electronegative. Intramolecular hydrogen bonding with the pseudo-π electrons of the cyclopropyl ring is another interaction that will stabilize the synclinal forms in some of these compounds, for example, X = OH, SH, SeH, NH 2 , and PH 2 . Further examples are discussed in a review …”

Synthesis, Microwave Spectrum, Quantum Chemical Calculations, and Conformational Composition of a Novel Primary Phosphine, Cyclopropylethynylphosphine, (C3H5C≡CPH2)

“…These studies include CH 3 PH 2 , (CH 3 ) 2 PH, , (CH 3 ) 3 CPH 2 , (CH 3 ) 3 P, (CH 3 ) 2 CHPH 2 , CH 3 CH 2 PH 2 , , cyclopropylphosphine (C 3 H 5 PH 2 ), phenylphosphine (C 6 H 5 PH 2 ), H 2 PCH 2 CH 2 CN, HCCPH 2 , H 2 CCHPH 2 , , H 2 PCH 2 CH 2 PH 2 , HCCCH 2 PH 2 , H 2 CCHCH 2 PH 2 , H 2 CCCHPH 2 , phosphirane (C 2 H 5 P), cyclopropylmethylphosphine (C 3 H 5 CH 2 PH 2 ), cyclopentadienylphosphine (C 5 H 5 PH 2 ), (chloromethyl)phosphine (ClCH 2 PH 2 ), and (2-chloroethyl)phosphine, (ClCH 2 CH 2 PH 2 ) . While one conformer exists for most of these phosphines, the existence of two or more rotameric forms have been seen for each of CH 3 CH 2 PH 2 , , H 2 PCH 2 CH 2 CN, H 2 PCH 2 CH 2 PH 2 , H 2 CCHCH 2 PH 2 , H 2 CCCHPH 2, C 3 H 5 CH 2 PH 2 , C 5 H 5 PH 2 , and ClCH 2 PH 2 . A comparison of the structural and conformational properties of amines and phosphines has recently been investigated in a gas electron-diffraction and quantum chemical study, which concluded that these properties are often different for phosphines and their amine analogues …”