Abstract
| I. | Introduction | 347 |
| II. | Gas‐Phase Ion–Molecule Reactions | 348 |
| III. | Scope and Applications of Gas‐Phase Base‐Induced 1,4‐Elimination | 349 |
| | A. Anionic and Cationic 1,4‐Elimination | 349 |
| | B. Anionic 1,4‐Elimination in an FT‐ICR Cell | 350 |
| | C. Anionic 1,4‐Elimination in an FA Flow Tube | 351 |
| IV. | Stereochemistry of 1,4‐Elimination | 352 |
| | A. Syn Versus Anti Stereochemistry | 352 |
| | B. Effect of E Versus Z Stereochemistry of the Substrate | 353 |
| V. | Mechanism of 1,4‐Elimination: E1cb Versus E2 | 353 |
| | A. Base‐Induced 1,4‐Elimination of 1‐Alkoxy‐2‐Butenes | 353 |
| | B. Base‐Induced 1,4‐Elimination of 3‐Alkoxycyclohexenes | 354 |
| | C. New DFT Computations on Base‐Induced 1,4‐Eliminations | 354 |
| VI. | Conclusions and Outlook | 358 |
| Acknowledgment | 359 |
| References | 359 |
Experimental and theoretical studies on gas‐phase base‐induced 1,4‐elimination reactions are summarized and discussed. The emphasis is on the synergy that is achieved by combining the complementary data from mass spectrometry and theoretical chemistry. The scope and applications of 1,4‐eliminations are discussed and compared with other elementary reactions; e.g., 1,2‐elimination and aliphatic (S~N~2) and allylic (S~N~2′) nucleophilic substitution. Furthermore, the syn versus anti stereochemistry of 1,4‐elimination reactions and the effect of E versus Z stereochemistry of the substrate are examined. Particular attention is paid to the mechanistic nature of 1,4‐elimination, i.e., E2 or E1cb, as well as special features such as the single‐well E2 and E1cb mechanism. Also, new results from density functional theory computations (BP86/TZ2P) are presented. © 2002 Wiley Periodicals, Inc., Mass Spec Rev 20:347–361, 2001; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mas.10007