Calculation of Rotational Barriers of 4-Acyloxy-4’-N-N-Butylcarbamyloxy-Biphenyls by Molecular Calculation and Linear Free Energy Relationships
Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2019, Vol 13, Issue 1
Abstract
Rotational barriers of ten 4-acyloxy-4’-N-n-butylcarbamyloxy-biphenyls were calculated by density functional theory. Linear free energy relationships between rotational barriers and reduced mass existed in these compounds. Rotational barriers of these compounds from dihedral angle of 450 to 900 (9E0Δ ’s) were linearly correlated with the inverse of reduced mass (1/m’). Thus, this rotational mechanism was just a simple physical rotation of an object about its center axis. On the other hand, rotational barriers of these compounds from dihedral angle of 450 to 00 ( E0Δ’s)) were dependent upon both 1/m’ and the vibrational energy difference at the C(1)-C(1’) bond near dihedral angle of 00(*σ’s). Values of ()( 1/2vibvibEE=Δ= were linearly correlated with the inverse of the root of reduced mass (1/√m’). Thus, the Δ E0 values calculated from density functional theory combined both physically rotational energy barrier, ΔE90, and vibrational (or stretching) energy barrier, vibEΔ. A two-step mechanism for the rotation of biphenyl from dihedral angle of -450 to 450 through the intermediate with an increasing C(1)-C(1’) pivot bond length of 0.027Ǻ was proposed. Accordingly, values of the bond length incensement of these ten biphenyls were calculated to be from 0.037 to 0.046 Ǻ. Thus, the experimental ΔE0 values were estimated to be the calculated ΔE0 values minus the vibEΔ values. One of the paradoxical results in Chemistry was that the rotational barriers of biphenyls obtained from experiments were significant different to those calculated by quantum mechanism. In the gas-phase experiments, Bastiansen and Samdal estimated the barriers from ground state (dihedral angle, φ= 450) to φ= 00 and φ= 90o to be 0 6.02.1E=Δ±kJ/mol and 90 6.52.E0Δ=±kJ/mol, respectively [1]. Theoretical calculation for rotation barriers of biphenyl by different levels of basis sets of quantum mechanism was always active in this field since the second half of last century. Tsuzuki and Tanabe reported E0Δ = 13.93 kJ/mol and 9E0Δ= 6.32 kJ/mol from HF/6-31G** level of quantum mechanism calculation [2]. Rubio et al. found E0Δ= 12.93 kJ/mol and 9E0Δ= 6.40 kJ/mol from 4s3p1d/2s1p basis set level of quantum mechanism calculation [3]. Karpfen et al. estimated that the E0Δvalues were 13.8, 16.3, and 8.4 kJ/mol and that the 9E0Δvalues were 6.3, 7.5, and 10.0 kJ/mol by SCF, MP2, and B3LYP methods, respectively [4].
Authors and Affiliations
Shu-Hsien Lin, Yu-Fang Shen, Chun-Yu Chiou, Gialih Lin, Gan-Hong Chen
Keywords
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- EP ID EP585876
- DOI 10.26717/BJSTR.2019.13.002332
- Views 144
- Downloads 0
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