S_N1, E1, and E2 Reactions oftert-Amyl Compounds: Improved Analysis Using Computational Chemistry and ASAP-HSQC NMR Spectroscopy

Abstract

A set of inexpensive and pedagogically rich experiments focusing on S N 1, E1, and E2 reactions have been updated to include modern computational and spectroscopic analyses. The S N 1 experiment involves treatment of tert-amyl alcohol with hydrochloric acid to generate the corresponding alkyl chloride, which is used as the starting material for the subsequent E2 reaction. The E1 experiment involves reaction of tert-amyl alcohol with sulfuric acid. Both elimination reactions generate a pair of isomeric methylbutenes, with the ratio being dependent on the reaction mechanism. The combination of computational chemistry and a recently developed fast heteronuclear single-quantum correlation spectroscopy method (ASAP-HSQC), in tandem with 1 H and 13 C NMR and GC−MS analysis, allows the E1 and E2 product mixtures to be fully analyzed by students.

WebMO: Web‐based computational chemistry calculations in education and research

“…WebMO can be used to provide computational and visual explanations of many concepts in organic chemistry courses and laboratories 72–83 :…”

An Improved Mechanistic Interpretation of the Acid-Catalyzed Dehydration of Methylcyclohexanols

“…The dehydration of methycyclohexanols is similar to the sulfuric acid-catalyzed dehydration of 2-methyl-2-butanol and 3-methyl-2-butanol (Scheme 4). 15 The isoamylene products were collected by distillation without prior reflux. For the dehydration of 2-methyl-2-butanol, only two alkene isomers were detectable via GC−MS analysis of the distillate with student results consistently showing 85−89% 2-methyl-2butene and 11−15% 2-methyl-1-butene.…”

“…Despite these simple reactions being a common fixture in organic laboratory curricula, featured in laboratory textbooks, , and having inspired multiple educational implementations, − a coherent conceptual description has so far not been communicated. Herein, similar to other dehydration reactions, , we present computational and modern spectroscopic techniques to clarify the mechanistic description of the acid-catalyzed dehydration of 1 .…”

Expanding the Scope of an Electrophilic Aromatic Substitution Discovery Experiment Including Hydride and Methyl Shifts

“…27 Faculty may consider options for mining textbooks 28 or the research literature 29 for descriptions of carbocations, including analysis of their stabilizing features such as resonance, hyperconjugation, and induction; in many cases these are supported by computational chemistry approaches. 30,31 Hydride and alkyl shifts have been explored in a range of experimental and theoretical contexts 32 as detailed below, notably with a treatise in this Journal of the historically important methyl shift found in the Wagner-Meerwein rearrangement. 33 However, among the many reactions that have been explored in the undergraduate laboratory, only a handful of experiments involve carbocation rearrangements.…”

“…Carbocations and their behavior also continue to fascinate, in part due to the provocative history of nonclassical carbocation structures including the isobornyl system . Faculty may consider options for mining textbooks or the research literature for descriptions of carbocations, including analysis of their stabilizing features such as resonance, hyperconjugation, and induction; in many cases these are supported by computational chemistry approaches. , Hydride and alkyl shifts have been explored in a range of experimental and theoretical contexts as detailed below, notably with a treatise in this Journal of the historically important methyl shift found in the Wagner-Meerwein rearrangement …”