Topic
Substituent
About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.
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TL;DR: Several factors affecting reactivity in ammonia chemical ionization mass spectrometry (NH3 CI) have been examined as discussed by the authors, including sample proton affinity, the preferred site of protonation and [NH4]+ attachment, and substituent effects.
Abstract: Several factors affecting reactivity in ammonia chemical ionization mass spectrometry (NH3 CI) have been examined. These include the sample proton affinity, the preferred site of protonation and [NH4]+ attachment, and substituent effects. In general, compounds having proton affinities ≲787 kJ mol−1 do not yield analytically useful intensities of the [M·NH4]+ adduct ion. Substituted aromatic compounds in which the ring is the most basic site yield little (if any) [M·NH4]+ ion even if the proton affinity of the compound is greater than 787 kJ mol−1. On the other hand, some aromatic compounds in which the substituent is the most basic site yield relatively abundant adduct ions. The spectra of compounds possessing a good leaving group (X) exhibit only weak [M·NH4]+ ions, but intense [M·NH4 − HX]+ and [M − X]+ ions formed by substitution and elimination reactions. Electronic effects strongly influence these processes. Several examples are presented in which isomers are readily differentiated because of different reactivities under ammonia chemical ionization conditions.
98 citations
TL;DR: A mild, versatile, and convenient method for efficient intramolecular oxytrifluoromethylthiolation of unactivated alkenes catalyzed by Cu(OAc)2 has been developed.
98 citations
TL;DR: In this paper, the stereochemistry of propylene insertion/propagation reactions with a variety of Cs and C1 symmetric, bridged cyclopentadienyl-fluorenyl ligands containing metallocene catalysts is discussed.
98 citations
TL;DR: In this paper, rate studies of benzene and related alkoxy-substituted aromatics by n-BuLi/TMEDA mixtures implicate similar mechanisms in which the proton transfers are rate limiting with transition structures of stoichiometry.
Abstract: Rate studies of the lithiation of benzene and related alkoxy-substituted aromatics by n-BuLi/TMEDA mixtures implicate similar mechanisms in which the proton transfers are rate limiting with transition structures of stoichiometry [(n-BuLi)2(TMEDA)2(Ar−H)]⧧ (Ar−H = benzene, C6H5OCH3, m-C6H4(OCH3)2, C6H5OCH2OCH3, and C6H5OCH2CH2N(CH3)2). Cooperative substituent effects and an apparent importance of inductive effects suggest a mechanism in which alkoxy−lithium interactions are minor or nonexistent in the rate-limiting transition structures. Supported by ab initio calculations, transition structures based upon triple ions of general structure [(n-Bu)2Li]-//+Li(TMEDA)2 are discussed.
98 citations
98 citations