J.F. Sullivan

Far infrared and low frequency gas phase Raman spectra and conformational stability of the 1‐halopropanes

The far infrared (375–50 cm−1) and low frequency Raman (400–70 cm−1) spectra of the gaseous 1‐halopropanes CH3CH2CH2F, CH3CH2CH2Cl, and CH3CH2CH2Br have been recorded and both the methyl and asymmetric torsional modes have been observed and assigned for both the gauche and trans conformers for all of these molecules. The asymmetric torsions for each molecule have several observed excited states which fall on the low frequency side of the fundamental. The asymmetric torsional potential functions have been calculated and, from these potential functions, the enthalpy differences between the high energy trans and low energy gauche conformers have been determined to be 122±10 cm−1 for the fluoride, 127±10 cm−1 for the chloride, and 37±10 cm−1 for the bromide. The trans and gauche methyl torsions have also been observed and assigned for the three 1‐halopropanes. The resulting barriers in cm−1 are: 936±4 (trans), 986±9 (gauche) for 1‐fluoropropane; 929±2 (trans), 1080±3 (gauche) for 1‐chloropropane; and 841 (tra...

Electron diffraction investigation of the molecular structures of ethyl isocyanate and ethyl isothiocyanate

Abstract Electron diffraction (ED) measurements and published microwave spectra are used to define the molecular structures of ethyl isocyanate and ethyl isothiocyanate in the gas phase. A cis -conformation is compatible with the data in both cases, while ED data for EtNCO are also consistent with a deviation of 45° from the cis conformation. An interpretation (in general terms) of the very complex microwave spectra in terms of an anharmonic two-dimensional motion combining the bend at nitrogen and the CN torsion is proposed. An average cis structure ( r * av basis) consistent with ED and microwave data with removal of the effects of the torsional motion is proposed in each case, with skeletal parameters (NCO, NCS) r CN 144.8 pm, 143.8; r CC 152.4, 152.0 pm; r NC 121.8 pm, 118.7; r CO 117.4 pm, r CS 158.0 pm; ∠CCN 114.7°, 111.0°; ∠CNC 132.2°, 147,4°; ∠NCO 192.2°, ∠NCS 184.5°.

Microwave, infrared and Raman spectra, conformation, and vibrational assignment of isopropylisocyanate

Abstract The low resolution microwave spectrum of isopropylisocyanate, (CH 3 ) 2 CHNCO, has been recorded from 18.0 to 39.0 GHz. From the spacing of the major transitions it is shown that the value of 4031 MHz for B + C is consistent with the skew conformer with a CNC angle of ca. 139° where the NCO moiety is eclipsing one of the methyl groups, although the trans conformer where the lone pair of electrons on the nitrogen is eclipsing the hydrogen atom cannot be entirely ruled out. The infrared (3200-50 cm −1 ) and the Raman (3300-20 cm −1 ) spectra have been recorded for gaseous and solid isopropylisocyanate. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization values measured. There is little indication of the presence of a second conformer at ambient temperature from a comparison of the vibrational data for the fluid and solid phases. A complete vibrational analysis, based on infrared band contours, depolarization values and group frequencies, is proposed. The two methyl torsions have been observed in the Raman spectrum of the solid at 278 and 257 cm −1 and from these data the barrier to internal rotation was calculated to be 1620 cm −1 (4.63 kcal mol −1 ). These results are compared with similar quantities for some corresponding molecules.

Infrared and Raman spectra and normal coordinate calculations for methylisothiocyanate

Abstract The infrared spectra (3200-50 cm −1 ) of gaseous and solid CH 3 NCS and CD 3 NCS and the Raman spectra (3200-10 cm −1 ) of the liquids and solids have been recorded. The spectra have been interpreted on the basis of a “pseudo-symmetric top” with C 3v symmetry. An assignment of the fundamental vibrations in both molecules, based on their infrared band contours, depolarization values and group frequencies, is given and discussed. Particularly interesting is the low-frequency region where band maxima were observed at 152 and 80 cm −1 for CH 3 NCS and 139 and 71 cm −1 for CD 3 NCS in the infrared spectra of the gases. A normal coordinate analysis has also been carried out based on C 3v symmetry. Considerable mixing was found between the C α N stretch and NCS symmetric stretch in both isotopic species. The other normal modes in CH 3 NCS are reasonably pure but, for the CD 3 NCS molecule, considerable mixing was found between the CD 3 stretches and NCS antisymmetric stretch. The proposed vibrational assignment and the results of the normal coordinate calculations are discussed and compared with the results obtained for similar molecules.

Electron diffraction investigation of the molecular structures of isopropyl isocyanate and isopropyl isothiocyanate

Abstract The molecular structures of isopropyl isocyanate and isopropyl isothiocyanate have been determined by electron diffraction in the gas phase. For both molecules the data are consistent with the presence of a single conformer at room temperature, with the NCX group eclipsing one of the CC bonds of the isopropyl group (a skew conformation). The structures found are consistent with the limited information available from microwave studies. The skeletal parameters found are (NCO, NCS; distances in pm, angles in degrees): r (CN) 146.0(8), 145.9(13); r (CC) 153.4(5), 15.8(7); r (NC) 121.4(6), 120.1(6); r (CO) 118.4(4); r (CS) 159.8(5); ∠NCC 110.0(5), 110.4(10); ∠CCC 114.7(9), 115.7(13); ∠CNC 132.6(10), 135.9(17); ∠NCX 159(3), 166(3); CN torsion 125(3), 115(6) (where a torsion angle of 120° corresponds to the skew form). The results are compared with those for some related molecules.

Infrared and Raman spectra, vibrational assignment and normal coordinate calculations for ethylisothiocyanate-d0 and -d5

Abstract The i.r. spectra (3500-40 cm−1) of gaseous and solid ethylisothiocyanate, CH3CH2NCS, and ethylisothiocyanate-d5, CD3CD2NCS, and the Raman spectra (3200-10 cm−1) of the liquids and solids have been recorded. Additionally, the i.r. spectrum of matrix (N2) isolated CH3CH2NCS was recorded from 3500 to 200 cm−1. The vibrational spectra have been interpreted on the basis of a cis form of Cs symmetry for all three physical states; however, in the spectum of the matrix isolated sample at 10 K, several of the fundamentals are doublets which may be arising from two conformers at this temperature. A vibrational assignment is given based on i.r. band contours, depolarization values, isotopic shifts and group frequencies. The assignment is supported by the Teller—Redlich product ratios. The methyl torsion was observed at 270 cm−1 in the solid phase which gives a periodic barrier of 4.7 kcal/mole. A normal coordinate calculation has been carried out utilizing a modified valence force field consisting of 15 diagonal force constants and seven interaction terms which reproduced the observed frequencies with an error of 1.45% for the -d0 molecule and 3.40% for the -d5 compound. Because of the large CNC angle (∼ 145°) and low barrier to internal rotation of the asymmetric rotor, the skeletal bend and torsion couple to give a very broad band with two maxima and apparent P band heads. These results are compared to corresponding studies of similar molecules.

Vibrational assignment of 1,4-diphenylbutadiyne

Abstract Infrared and Raman spectra in the region 3500–40 cm −1 were recorded for solutions crystalline solid of 1,4-diphenylbutadiyne (diphenyldiacetylene) at room temperature. The fundamental frequencies were assigned according to D 2h symmetry. The results of a normal coordinate analysis are based on the valence force field obtained for 1,4-diphenylbutadiyne, diphenylethyne (diphenylacetylene), phenylethyne, benzene and simultaneously for some of their deuterated isotopomers.

Raman and infrared spectra and ab initio calculations for the determination of the conformational stability for fluorocarbonyl and acetyl isocyanate

Abstract The infrared and Raman spectra of gaseous, liquid and solid fluorocarbonyl isocyanate, FC(O)NCO, and acetyl isocyanate, CH 3 C(O)NCO, have been recorded. From these data the conformational stability has been determined for both molecules for all three physical states. The conformational energy differences, optimized geometries, and fundamental vibrational frequencies have also been obtained from ab initio calculations.

Low frequency vibrational spectrum and conformational analysis of allylamine

Abstract The Raman spectra of gaseous, liquid and solid allylamine and allylamine-N-d2 as well as the i.r. spectra of these gases and solids have been recorded from 3500 to 50 cm−1 with special emphasis on the low frequency spectral region. The fundamental of the vinyl asymmetric torsion of the cis—trans conformer (vinyl moiety cis to the nitrogen atom and the lone electron pair on the nitrogen atom trans to the methylene hydrogens) of CH2CHCH2NH2 was observed at 170.3 cm−1 with two accompanying hot bands and the corresponding torsion of the gauche—trans conformer has been observed at 110.4 cm−1, again with two accompanying hot bands, in the i.r. spectrum of the gas. From these data the potential function for internal rotation of the asymmetric vinyl top has been determined and the following potential constants have been evaluated: V2 = 462 ± 29, V3 = 954 ± 12, V4 = 57 ± 8 and V6 = −58 ± 5cm−1. It has been determined that the cis—trans conformer is the most stable form at ambient temperature in the gas phase and the enthalpy difference between the cis—trans and the gauche-trans conformers is 340 ± 20cm−1 (972 ± 57 cal/mol) for the vapor. This value is consistent with a temperature study of the i.r. spectrum of the vapor. Additionally the vinyl asymmetric torsion for one of the gauche—gauche conformers was observed at 122.9cm−1 with tentative assignments given for this torsional mode for the other two conformers. The fundamental amino torsions for four of the conformers have been observed at 275,252,242 and 228 cm−1 for CH2CHCH2NH2 which shift with deuteration of the amino group to 209, 197, 185 and 171 cm−1; tentative assignments of these bands to the individual conformers are also proposed. The vibrational spectra of allylamine and allylamine-N-d2 have been reinvestigated in view of the additional Raman gas phase data, and normal coordinate calculations have been carried out. These results are discussed and compared with the previous studies.

Structure, vibrational assignment, normal coordinate analysis, and ab initio calculations of methylisocyanate☆

The infrared (3200-30 cm−1) and Raman (3200-10 cm−1) spectra of gaseous and solid methylisocyanate, CH3NCO, have been recorded. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization ratios have been measured. The CNC bend has been observed in the far infrared and low frequency Raman spectra of the gas at approximately 172 cm−1. An additional far infrared band at ≈50 cm−1 has tentatively been assigned as the methyl torsional mode, although it could be due to the Δν = 1, Δl = ± 1 transitions of the CNC bending mode. A complete assignment of the vibrational fundamentals is proposed. The structural parameters, force constants, and vibrational frequencies have been determined from ab initio Hartree—Fock gradient calculations using the 6-31G* basis set. Additionally, structural parameters have been obtained with the 6-311 + + G** basis set with electron correlation at the MP2 level which are compared to those obtained from the microwave data and electron diffraction study. These results are compared with the corresponding quantities obtained for similar molecules.