Conformational analysis of amphetamine free base (I), amphetamine•HC1 (II), methamphetamine•HC1 (III), o-methoxymethamphetamine• HC1 (IV), and benzphetamine HC1 (V) by high-resolution nmr spectroscopy has demonstrated a high preference for the írans-phenylamino rotamers (la, Illa, IVa, Va) in aq solution. Since the same trans conformational preference was recently established for norepinephrine (NE), the prototype for aadrenergic catecholamines, this structural evidence is compatible with the increasingly popular view that amphetamines may exert their pharmacological activity as a-adrenergic agonists. Evidence has been obtained for the first time that intramolecular H bonding occurs in methoxyphenamine • HC1 (IV) between an ammonium proton and the O of the o-OMe substituent. Amphetamine•HC1 (II) was found to give a "deceptively simple" ABC
random noise generator, were described earlier.3 The chemical shifts reported here have been corrected to carbon disulfide as external reference by the relations 5c = 5cdioxs"e + 125.5 ppm, or 5c = 5cch2ci2 -(-138.9 ppm, and were reproducible to ±0.1 ppm. In the 3-methylcyclopentanols, the assignments of the carbons 3 and 4 are somewhat uncertain. The same is true of C-3, C-4, and C-5 in the 3-methylcyclopentyl acetates because the resonances are very close together.
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