J(F,H), J(C,H) and J(H,H) couplings involving the individual methyl group protons in 1,2,3,4-tetrachloro-5,6,7,8-tetrafluoro-9-methyltriptycene. Evidence of blue-shifting hydrogen bond.
1,2,3,4-tetrachloro-5,6,7,8-tetrafluoro-9-methyltriptycene was studied in NMR spectra at low temperatures where the methyl group dynamics is frozen. Values of 5J(19F,1H), 1J(13C,1H), and 2J(1H,1H) for the individual methyl protons were measured. They are in a fair agreement with the corresponding theoretical values calculated at a density functional theory (DFT) level. The 5J(19F,1H) couplings involve the peri-F nucleus and occur via the 'through space' mechanism. Both the natural bond orbital analysis (at a HF level) and the observed pattern of 1J(13C,1H) coupling values corroborate occurrence in this molecule of intramolecular, blue-shifting hydrogen bonds engaging the methyl hydrogens. The 'through space' 5J(19F,1H) couplings may indicate the routes of electron density transfers that escape detection by the natural bond analysis. A consideration of these effects can enrich the chemical intuition involving this specific sort of H-bonds.
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
I
I
Czerski
K
K
Kamieńska-Trela
W
W
Koźmiński
T
T
Ratajczyk
S
S
Szymański
J
J
Wójcik
D000873:Anthracenes / Q000737:chemistry*; D003198:Computer Simulation; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards*; D008956:Models, Chemical; D008968:Molecular Conformation; D012015:Reference Standards; D012680:Sensitivity and Specificity
C526243:1,2,3,4-tetrachloro-5,6,7,8-tetrafluoro-9-methyltriptycene; D000873:Anthracenes