SolomonsLKChapter7

SolomonsLKChapter7 - Chapter 7 Alkenes and Alkynes I:...

Info iconThis preview shows pages 1–14. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 7 Alkenes and Alkynes I: Properties and Synthesis Elimination Reactions of Alkyl Halides
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The Cahn-Ingold-Prelog convention is used to assign the groups of highest priority on each carbon If the group of highest priority on one carbon is on the same side as the group of highest priority on the other carbon the double bond is Z (zusammen) If the highest priority groups are on opposite sides the alkene is E (entgegen) The ( E )-( Z ) System for Designating Alkene Diastereomers
Background image of page 2
Name this compound A. E-2-chloro-3-methyl-2-pentene B. Z-2-chloro-3-methyl-2-pentene C. Z-2-chloro-3-ethyl-2-butene D. None of these C C Cl H 3 C CH 2 CH 3 CH 3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This compound is A. E diastereomer B. Z diastereomer C. Chiral D. Neither E nor Z CH 3 Br
Background image of page 4
l Generally cis alkenes are less stable than trans alkenes because of steric hinderance l Heat of Hydrogenation The relative stabilities of alkenes can be measured using the exothermic heats of hydrogenation Relative Stabilities of Alkenes
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Heats of hydrogenation of three butene isomers Since product is the same, the difference in H are due to the alkene
Background image of page 6
The greater the number of attached alkyl groups ( i.e . the more highly substituted the carbon atoms of the double bond), the greater the alkene ʼ s stability Overall Relative Stability of Alkenes
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Dehydrohalogenation l Reactions by an E2 mechanism are most useful E1 reactions can be problematic l E2 reaction are favored by: Secondary or tertiary alkyl halides Alkoxide bases such as sodium ethoxide or potassium tert - butoxide l Bulky bases such as potassium tert -butoxide should be used for E2 reactions of primary alkyl halides Synthesis of Alkenes via Elimination Reactions
Background image of page 8
Zaitzev ʼ s Rule: when two different alkenes are possible in an elimination, the most highly substituted alkene will be the major product This is true only if a small base such as ethoxide is used Zaitsev’s Rule: Formation of the Most Substituted Alkene Some hydrogen halides can eliminate to give two different alkenes
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
t T.S. refects greater stability oF more substituted double bond t Example oF Kinetic control : When one oF two products is Formed because its Free energy oF activation is lower and thereFore the rate oF its Formation is Faster Basis of Zaitsev ` s Rule: Transition state has double bond character
Background image of page 10
Bulky bases such as potassium tert -butoxide have difFculty removing sterically hindered hydrogens and generally only react with more accessible hydrogens (e.g. primary hydrogens) Formation of the Least Substituted Alkene Using a Bulky Base
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
All four atoms (H-C-C-L) must be in the same plane t Anti coplanar orientation is preferred so all atoms are staggered t In a cyclohexane ring the eliminating substituents must be diaxial to be anti coplanar The Stereochemistry of E2 Reactions Syn coplanar in some rigid systems
Background image of page 12
Neomenthyl chloride and menthyl chloride give different elimination products with sodium ethoxide Example of stereochemical requirements
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 14
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 48

SolomonsLKChapter7 - Chapter 7 Alkenes and Alkynes I:...

This preview shows document pages 1 - 14. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online