Microwave Spectrum, Conformational Composition, and Intramolecular Hydrogen Bonding of (2-Chloroethyl)amine (ClCH₂CH₂NH₂)

Abstract

The microwave spectrum of (2-chloroethyl)amine, ClCH(2)CH(2)NH(2), has been investigated in the 22-120 GHz region. Five rotameric forms are possible for this compound. In two of these conformers, denoted I and II, the Cl-C-C-N chain of atoms is antiperiplanar, with different orientations of the amino group. The link of the said atoms is synclinal in the three remaining forms, III-V, which differ with respect to the orientation of the amino group. The microwave spectra of four of these conformers, I-IV, have been assigned. In two of these rotamers, III and IV, the amino group is oriented in such a manner that rare and weak five-membered N-H···Cl intramolecular hydrogen bonds are formed. The geometries of conformers I and II preclude a stabilization by this interaction. The energy differences between the conformers were obtained from relative intensity measurements of spectral lines. The hydrogen-bonded conformer IV represents the global energy minimum. This rotamer is 0.3(7) kJ/mol more stable than the other hydrogen-bonded conformer III, 4.1(11) kJ/mol more stable than II, and 5.5(15) kJ/mol more stable than I. The spectroscopic work has been augmented by quantum chemical calculations at the CCSD/cc-pVTZ and MP2/6-311++G(3df,3pd) levels of theory. The CCSD rotational constants and energy differences are in good agreement with their experimental counterparts.

Energy decomposition analysis of gauche preference in 2-haloethanol, 2-haloethylamine (halogen = F, Cl), their protonated forms and anti preference in 1-chloro-2-fluoroethane

“…13c The same applies to CEA, for which aa and ag conformers differ by 0.17 kcal mol À1 in our calculations. Conformers ga-CEA and gg-CEA also have similar energies which is in accord with previous experimental and theoretical data, 20 although their relative stability order is reversed in our MP2 calculations. The relative energies for other three conformers of CEA are in agreement with the exisiting data.…”

“…The relative energies for other three conformers of CEA are in agreement with the exisiting data. 20 As in the case of 2-haloalcohols, the gauche preference in amines is smaller when halogen is chlorine atom. Decomposition of the total binding energy between the two XCH 2 c and cCH 2 NH 2 radical fragments into its components is given in Table 7, along with the decomposition of energy change occurring upon anti / gauche rotation of the heavy atom chain.…”

“…17 The replacement of uorine with chlorine atom in DFE results in a loss of gauche preference in 1-chloro-2-uoroethane (CFE) in the gas phase. 3a,12d,18 The same replacement in FE and FEA retains the gauche preference in 2-chloroethanol (CE) 12d,f,g,19 and 2-chloroethylamine (CEA), 20 but decreases the energy differences between gauche and anti forms relative to those for uorine compounds. In both CE and CEA, the dominance of gauche conformers has been attributed to stabilizing intramolecular hydrogen bonding interactions 19a usually described as an electrostatic attraction between antiparallel C-Cl and O(N)-H bond dipoles.…”

The structure of tris(chloromethyl)amine in the gas phase using quantum chemical calculations and gas electron diffraction and as a solid and melt using Raman spectroscopy

“…To obtain a measure for the dihedral dC2-N1-C4-Cl11, which is characteristic of the configuration adopted, twenty-two least-squares refinements have been carried out with dC2-N1-C4-Cl11 set to values greater than and less than that associated with the ideal synperiplanar configuration to give a series of RG/RG,Min. datapoints, presented in rC4-Cl11 = 183.0(2) pm} are somewhat longer than those calculated for analogous free molecules {NH2(CH2CH2Cl), rC(sp 3 )-Cl = 179.6 pm (CCSD/cc-pVTZ) [69]} in the gas phase. This is in harmony with the observations of Klapötke et al [1] for the single crystal, the earlier observations of Oberhammer et al…”

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. − …”