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Density Functional Theory Study of p‐tert ‐Butylcalix[4]crown‐7‐ether Ester Complexed with Alkylammonium Ions
Author(s) -
Eom Min Sik,
Ham Seung Wook,
Choe JongIn
Publication year - 2015
Publication title -
bulletin of the korean chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.237
H-Index - 59
ISSN - 1229-5949
DOI - 10.1002/bkcs.10101
Subject(s) - chemistry , density functional theory , conformational isomerism , ion , crystallography , hydrogen bond , ether , steric effects , natural bond orbital , proton affinity , computational chemistry , molecule , stereochemistry , organic chemistry , protonation
In this study, we describe the optimization of the three conformers (cone, partial cone, and 1,3‐alternate) of 1,3‐bridged p‐tert ‐butylcalix[4]crown‐7‐ether ester ( 1 ) using the density functional theory ( DFT ) B3LYP /6‐ 31G (d,p) method. 1 ( CONE ) was calculated to be the most stable of the three conformations of 1. The structures, energies, and frontier orbitals ( HOMO and LUMO ) of the exo ‐complexes of 1 ( CONE ) with alkylammonium ions were calculated using the DFT method. It was found that small alkylammonium cations exhibit a higher complexation efficiency with 1 than with larger alkylammonium ions. However, the branched alkylammonium ions exhibited stronger binding properties with 1 than the linear n ‐propyl and n ‐butyl ammonium ions. The DFT ‐calculated energies of 1 complexed with bulky alkylammonium ions exhibited stronger binding efficiencies than the calix[5]crown‐6‐ether ( 2 ). Hydrogen bonding and steric hindrance of the alkylammonium cations were found to be the primary factors governing the complexation efficiency of 1 with various cations. The DFT B3LYP /6‐ 31G (d,p)‐calculated IR spectra of the conformers of 1 and its cone‐type exo ‐complexes with various alkylammonium ions were subsequently analyzed. The hydrogen‐bonded NH and OH stretching vibrational frequencies were compared to the unrestricted vibrational frequencies in detail, and the unusually low NH stretching frequency (3054 cm −1 ) of the 1 ∙ iso‐Bu + complex and the unusually low OH stretching frequency (3387 cm −1 ) of the 1 ∙ n‐Bu + complex were determined to be caused by strong hydrogen bonding.