Mechanism of Nucleophilic Substitution

CCA! Volume 5

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Mechanism of Nucleophilic Substitution - SN1

The mechanism of nucleophilic substitutions (S_N1) is demonstrated.


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File: MOVIES/TRAM10/0321913.MOV

Voiceover
For this animation of an S_N1 reaction, the tetrahedral alkyl halide ionizes to form a planar, trigonal carbocation which may be attacked from either side by a nucleophile leading to racemization of a chiral halide.

Discussion
S_N1 (substitution nucleophilic first order) reactions involve ionization of the alkyl halide to form a carbocation. This step is the slow, rate determining step, of the reaction. The carbocation is then attacked by a nucleophile in a fast second step to form the product. The stereochemistry of this process is simulated with a model. The tetrahedral alkyl halide forms a planar, trigonal carbocation which may be attacked from either side by a nucleophile leading to racemization of chiral halides. The order of reactivity or tertiary > secondary > primary halides parallels the stability of the corresponding carbocations.

Citation:
	Silversmith, E. F.	J. Chem. Educ. 1988, 65, pp 70-73.

Design, Text and Demonstrator:
	Gary Trammell	University of Illinois at Springfield, Springfield, IL 62794

Videographer/Editor:
	Steve Dykema	University of Illinois at Springfield, Springfield, IL 62794

Voice:
	Margaret Biddle	University of Wisconsin - Madison, Madison, WI 53706

Audio Production:
	Greg Minix	University of Wisconsin - Madison, College of Engineering, Madison, WI 53706
	Jerrold J. Jacobsen	University of Wisconsin - Madison, Madison, WI 53706