Lecture 26 Ch.9 - CH310/318MSp.2011 Lecture26

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Lecture 26 Nucleophilic Substitutions: S N N 1 : : : Announcements : : : Homework 8 posted, due next Tues! Dr. Colapret teaching class on Thursday TA evaluations online (link in Bb) CH 310/318M – Sp.2011
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Last Time S N 2: nucleophilic substitution, bimolecular.  two limiting mechanisms for nucleophilic substitution in general A fundamental difference between them is the timing of bond-breaking and  bond-forming steps. V. Patman 2 CH 310/318M – Sp.2011 Tues 4.26.11 C Br H H H HO: - + C H H H HO Br δ - δ - Transition state with simultaneous  bond breaking and bond forming C H H H HO + Br : :: : : : :
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S N 2 Mechanistic evidence: Kinetics: the reaction rate is directly related to [E+] and [Nu-]. Labeling study: complete inversion of stereochemistry is observed V. Patman 3 CH 310/318M – Sp.2011 Tues 4.26.11 I C H I C 6 H 1 3 H 3 C H CH 3 C 6 H 1 3 I C I S N 2 acetone + 131 131 + (S)-2-Iodooctane (R)-2-Iodooctane
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S N 1 A different  mechanism:  bond breaking between carbon and the leaving  group is entirely completed before bond forming with the nucleophile  begins. This mechanism is designated S N 1 where S = substitution,  N = nucleophilic, 1 = unimolecular  Mechanism:  first  step is RDS V. Patman 4 CH 310/318M – Sp.2011 Tues 4.26.11 Evidence for S 1:
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This note was uploaded on 09/25/2011 for the course CH 318M taught by Professor Bocknack during the Spring '08 term at University of Texas at Austin.

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Lecture 26 Ch.9 - CH310/318MSp.2011 Lecture26

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