Microwave and Quantum Chemical Study of Intramolecular Hydrogen Bonding in 2-Propenylhydrazine (H₂C═CHCH₂NHNH₂)

Abstract

The microwave spectrum of 2-propenylhydrazine (H2C═CHCH2NHNH2) was studied in the 12-61 and 72-123 GHz spectral regions. A variety of intramolecular hydrogen bonds between one or more of the hydrogen atoms of the hydrazino group and the π-electrons are possible for this compound. Assignments of the spectra of four conformers, all of which are stabilized with intramolecular hydrogen bonds are reported. One hydrogen bond exists in two of these conformers, whereas the π-electrons are shared by two hydrogen atoms in the two other rotamers. Vibrationally excited-state spectra were assigned for three of the four conformers. The internal hydrogen bonds are weak, probably in the 3-6 kJ/mol range. A total of about 4400 transitions were assigned for these four forms. The microwave work was guided by quantum chemical calculations at the B3LYP/cc-pVTZ and CCSD/cc-pVTZ levels of theory. These calculations indicated that as many as 18 conformers may exist for 2-propenylhydrazine and 11 of these have either one or two intramolecular hydrogen bonds. The four conformers detected in this work are among the rotamers with the lowest CCSD electronic energies. The CCSD method predicts rotational constants that are very close to the experimental rotational constants. The B3LYP calculations yielded quartic centrifugal distortion constants that deviated considerably from their experimental counterparts in most cases. The calculation of vibration-rotation constants and sextic centrifugal distortion constants by the B3LYP method were generally found to be in poor agreement with the corresponding experimental constants.

Millimeter and submillimeter wave spectroscopy of propanal

“…The omission of F ac may influence the ability to determine higher order parameters or affect their values. Complications by describing molecules with two stable degenerate forms and necessary treatment of Coriolis interactions occurred already before [26,27]. For conformer I of cyanoacetaldehyde only transitions up to K a = 2 for 0 + and up to K a = 8 for 0 − -state are employed in the fit and moreover transitions with J equal to 30, 31, and 32 needed to be excluded [26].…”

“…For conformer I of cyanoacetaldehyde only transitions up to K a = 2 for 0 + and up to K a = 8 for 0 − -state are employed in the fit and moreover transitions with J equal to 30, 31, and 32 needed to be excluded [26]. For synclinal mercaptoacetonitrile, the standard deviation is four times larger than the expected experimental uncertainty and again special kinds of transitions were excluded, regarding large deviations between experimental and calculated frequencies [27]. For gauche propanal, a first model is now available into the submillimeter wave region.…”

Microwave and Quantum Chemical Study of Intramolecular Hydrogen Bonding in 2-Propynylhydrazine (HC≡CCH2NHNH2)

“…The second example is 2-propenylhydrazine (H 2 CCHCH 2 NHNH 2 ). 2 The spectra of four H-bonded conformers were assigned in this case. Two of these rotamers are stabilized with one H bond between one of the H atoms of the hydrazino group and the π-electrons of the double bond.…”

“…The microwave (MW) spectra of four conformers were assigned for this compound, and two of them were indeed stabilized by internal H bonds between one of the H atoms of the hydrazino group and the fluorine atom. The second example is 2-propenylhydrazine (H 2 CCHCH 2 NHNH 2 ) . The spectra of four H-bonded conformers were assigned in this case.…”

“…b See text. c Root-mean-square deviation defined as rms2 = ∑[(ν obs − ν calc )/u] 2 /(N − P), where ν obs and ν calc are the observed and calculated frequencies, u is the uncertainty of the observed frequency, N is the number of transitions used in the least-squares fit, and P is the number of spectroscopic constants used in the fit.Number of transitions used in the fit. The spectrum is listed in TableS14of the Supporting Information.The Journal of Physical Chemistry A…”