RESUMO
Recent X-ray crystallographic and NMR evidence indicates that relatively weak intramolecular edge-to-face interactions between aromatic rings can affect or determine the conformation of organic molecules in the solid state and in solution. Experimental estimates indicate that these interactions are energetically attractive by ca. 1.5 kcal mol(-1) but disfavored in solution by entropic factors due to the restricted internal mobility. Hence, these interactions are more manifest at low temperature in solution or in crystal structures where conformational entropy effects are negligible.
Assuntos
Derivados de Benzeno/química , Compostos de Bifenilo/química , Ácidos Carboxílicos/química , Dimerização , Éteres/química , Iminas/química , Conformação Molecular , Óxidos de Nitrogênio/química , EstereoisomerismoRESUMO
Three pre-column derivatization reagents, namely o-phthalaldehyde, 4-chloro-7-nitro-benz-2,1,3-oxadiazole, sodium naphthaquinone-4-sulphonate and two ion-pair reagents, namely, naphthalene-2-sulphonate and sodium dodecylsulphate have been investigated for their suitability for the qualitative and quantitative analysis of urine and plasma samples containing amphetamines. The derivatization method employing sodium naphthaquinone-4-sulphonate was found to be selective and sufficiently sensitive for the routine determination of amphetamine and methylamphetamine in urine and plasma samples at the ng/ml level.
