Infrared and nuclear magnetic resonance spectroscopic study of secondary amide hydrogen bonding in benzoyl PABA derivatives (retinoids).
Attenuated total reflection (ATR) Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) data are used to characterize the hydrogen bonding of the secondary amide N-H group of several structurally similar benzoyl derivatives of p-aminobenzoic acid esters (retinoids) in chloroform solution. The amide N-H can form intermolecular hydrogen bonds to several proton acceptors in these molecules or it can form an intramolecular hydrogen bond to a fluorine or oxygen atom in some of the molecules. The concentration dependence of the solution N-H infrared absorption bands is used to determine the formation of intramolecular and/or intermolecular H-bonds. Proton NMR spectra were obtained from deuterated chloroform solutions and the sec-amide N-H resonance was assigned for each compound. The downfield shift in the N-H resonance is correlated to intramolecular H-bond formation. Also, the NMR spectra of fluorine-containing compounds provide J(F-H) through-space coupling values. Using infrared and NMR data, the relative intramolecular hydrogen bond strengths (N-H...F or N-H...O) of the compounds are approximately ranked.
Dalterio
Richard
R
Bristol-Myers Squibb Company, Pharmaceutical Research Institute, Wallingford, Connecticut 06492, USA. richard.dalterio@bms.com
Huang
Xiaohua Stella
XS
Yu
Kuo-Long
KL
D000577:Amides / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D012176:Retinoids / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D062366:para-Aminobenzoates
D000577:Amides; D012176:Retinoids; D062366:para-Aminobenzoates