Substituent steering of dihedral angles around single bonds: the case of succinonitrile

Abstract

Succinonitrile is a material of plastic crystal nature arising from the low energy barrier between synclinal and antiperiplanar isomerization around the central C-C bond, while its high polarity makes it an efficient solvent for a wide variety of salts including ionic liquids. A prediction of the equilibrium dihedral angle - in the absence of experimental data - suffers from the shallow potential energy curve and electron diffraction results contain large standard errors. Here, to provide accurate structural data, the Fourier transform microwave spectrum and the mm-wave spectrum of the major isotopologues of synclinal succinonitrile have been measured, assigned and fitted to produce rotational, centrifugal distortion and quadrupole coupling constants. The mm-wave spectrum of the (13)C and (15)N singly substituted isotopologues in natural abundance has been assigned together with that of the chemically singly substituted (2)H isotopologues. The resultant rotational constants have been used to calculate the substitution geometry for succinonitrile. All parameters and constants are compared with theoretical values computed at the B3LYP, MP2 and CCSD/cc-pVTZ levels of theory. The dihedral angle of succinonitrile, which is a strong driver of the plastic crystal nature of succinonitrile, is found to be 66(2)° best comparable to CCSD/cc-pVTZ predictions and noticeably different from the 60° expected without substituent effects.

Conformational Relative Stability and Thermal Properties of Succinonitrile in Gas and Condensed Phases: Using CCSD and DFT Calculations

“…Insitu powder diffraction of the solid phase at 150 K results of only bond lengths of the gauche isomer, agree well with the result in this work. [21] The dihedral angle, obtained by the highest level of theory CCSD/6-311G + (d) (65.7°), agrees with the results of other levels of theory and with the experimental results using FT-microwave spectroscopy [24] but has a significant difference with the ED measurement. [19] All geometrical parameters of HF, B3LYP, and MP2 levels of theory found by Umar and Morsy are very close to the result of M06 and CCSD methods used in this work.…”

“…All bond lengths and angles at different levels of theory are in good agreement and comparable to the experimental results. [19,24] The differences among bond lengths of the different levels of theory are in the range 0-0.017 Å. On the other hand, bond angle differences are ranged 0-1.1°.…”

“…[11][12][13][14][15][16][17] In the gas and condensed phases, succinonitrile has two conformers; one with the two nitrile groups in the trans position while the other in which they are in the gauche position. [18][19][20][21][22][23][24][25] Early experimental results using vibrational spectroscopy have deduced that in the gas phase the trans isomer is more stable than the gauche isomer by 1 kcal/mol. On the other hand, X-ray data suggests that in the solid-phase, the gauche conformer is more stable by 0.36 kcal/mol.…”

The millimeter-wave spectrum and astronomical search of succinonitrile and its vibrational excited states

“…Succinonitrile has been studied in the centimeter wave range, using a high resolution Fourier transform microwave pulsedsupersonic jet spectrometer, and in the millimeter wave region up to 72 GHz, using a Stark modulation spectrometer (Jahn et al 2014). The spectra of the 13 C and 15 N singly substituted isotopologues in natural abundance were also observed together with that of the chemically singly substituted deuterium isotopologues.…”

Crystal structure of catena-poly[tetraaqua-(μ2-succinonitrile-κ 2 N:N′)cobalt(II)] dinitrate, C4H12CoN4O10

“…Succinonitrile is a solid-state plastic crystal at ambient conditions, with molecules that have welldefined positions and disordered orientation in a crystal lattice [9,10]. The properties arising from the low energy barrier of rotation around the C-C bond of the two methylene groups which allows the isomerization transition of succinonitrile molecules between the synclinal and antiperiplanar conformer [11]. In the title compound, the asymmetric unit contains one half of a Co(II), one nitrate ion, one half-molecule of succinonitrile, and two water molecules.…”