NMR Studies of Crowded Diels–Alder Adducts of 3,6‐Dibromophencyclone withN‐(2,6‐Dialkylphenyl)maleimides. Hindered Rotations and Magnetic Anisotropy. Ab Initio Calculations for Optimized Structures of the Precursor Maleimides and Their Adducts with Phencyclone and 3,6‐Dibromophencyclone

Abstract

6,9-Dibromo-1,3-diphenyl-2H-cyclopenta[l]phenanthren-2-one (commonly known as 3,6-dibromophencyclone), 1b, reacted with N-(2,6-dimethylphenyl)maleimide, 2a; with N-(2,6-diethylphenyl)maleimide, 2b; and with N-(2,6-diisopropylphenyl)maleimide, 2c, respectively, to yield the corresponding Diels -Alder adducts, 4a -c. The adducts were extensively characterized by NMR (7 T) at ambient temperatures using one-and twodimensional (1D and 2D) proton and carbon-13 techniques for assignments. Slow exchange limit (SEL) spectra were observed, demonstrating slow rotations on the NMR timescales, for the unsubstituted bridgehead phenyl groups [C(sp 3 )-C(aryl sp 2 ) bond rotations] and for the 2,6-dialkylphenyl groups [N(sp 2 ) -C(aryl sp 2 ) bond rotations]. Substantial magnetic anisotropic shifts were seen in the adducts. For example, in the N-(2,6-dialkylphenyl) moieties of the adducts, one of the alkyl groups is directed "into" the adduct cavity, toward the phenanthrenoid portion, and these "inner" alkyl proton NMR signals were shifted upfield. Thus, in CDCl 3 , the inner methyl of adduct 4a exhibits a proton resonance at 20.05 ppm, upfield of tetramethylsilane (TMS); the inner ethyl group signals from 4b appear at 0.09 ppm (CH 2 , quartet) and 20.11 ppm (CH 3 , triplet); and the inner isopropyl group from 4c is seen at 20.10 ppm (methine, approx. septet) and, 20.28 ppm (CH 3 , doublet). Ab initio molecular modeling results are presented for the precursor maleimides, 2, and their adducts, 3, from the parent phencyclone, 1a, at the restricted Hartree-Fock level using the 6-31G Ã basis set. Results for the dibromoadducts, 4, used the LAV3P Ã basis set.

Forensic Science

“…Reviews on the forensic analysis of drugs have been published (721,722). Drugs and other substances of forensic interest have been analyzed by GC/MS (723-727), LC/ MS/MS (728-740), CE (741)(742)(743)(744), Raman spectroscopy (745)(746)(747)(748), HPLC (749-753), HPLC-ESI-MS (754), LC/TOFMS and LC/chemiluminescence nitrogen detector (755), GC × GC/ TOFMS (756), GC with retention time locking (757), GC/MS and GC/ECD (758), hydrophilic interaction chromatography-mass spectrometry (759), SPME and GC/MS (760-764), immunoassays (765-770), LC-ES-MS (771), overpressured-layer chromatography and GC/MS (772), GC/MS/MS (773), LC/TOFMS (774), HS-SPME and GC (775), NMR (776)(777)(778)(779), SPE and LC/ MS/MS (780), TLC (781), and SPME and LC/MS (782).…”