Chapter08notes

Chapter08notes - 1. Addition Reactions The characteristic...

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

View Full Document Right Arrow Icon
1 The characteristic reaction of alkenes is addition—the  bond is broken and two new  bonds are formed. 1. Addition Reactions Alkenes are electron rich, with the electron density of the  bond concentrated above and below the plane of the molecule. Therefore, alkenes act as nucleophiles and react with electrophiles. Simple alkenes do not react with nucleophiles or bases, reagents that are themselves electron rich.
Background image of page 1

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

View Full DocumentRight Arrow Icon
2 C C E Nu δ + δ - C C E + Nu 1. Addition Reactions
Background image of page 2
3 Because the carbon atoms of a double bond are both trigonal planar, the elements of X and Y can be added to them from the same side or from opposite sides. 1. Syn and Anti Addition to Alkenes
Background image of page 3

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

View Full DocumentRight Arrow Icon
4 1. Addition Reactions (some examples)
Background image of page 4
5 2. Hydrohalogenation—Electrophilic Addition of HX
Background image of page 5

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

View Full DocumentRight Arrow Icon
6 The mechanism of electrophilic addition consists of two successive Lewis acid-base reactions. 2. Mechanism of Hydrohalogenation C C A C C E C C Nu Nu E Nu δ + δ -
Background image of page 6
7 2. Energy Diagram
Background image of page 7

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

View Full DocumentRight Arrow Icon
8 C C H H H H E Nu E C C H H H H E C C H H H H E C C H H H H Nu E C C H H H H Nu Nu same  as same  as 3. Regioselectivity – Markovnikov’s Rule For symmetrical substrates, no problem for regiochemistry
Background image of page 8
9 Markovnikov’s rule states that in the addition of HX to an unsymmetrical alkene, the H atom adds to the less substituted carbon atom—that is, the carbon that has the greater number of H atoms to begin with. 3. Markovnikov’s Rule E Nu C C H H 3 C H H E C C H H CH 3 H E C C CH 3 H H H E C C CH 3 H H H Nu E C C H H CH 3 H Nu Nu Nu or different  from For unsymmetrical substrates:
Background image of page 9

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

View Full DocumentRight Arrow Icon
10 The basis of Markovnikov’s rule is the formation of a carbocation in the rate-determining step of the mechanism. In the addition of HX to an unsymmetrical alkene, the H atom is added to the less substituted carbon to form the more stable, more substituted carbocation. 3. Carbocation Stability and Markovnikov’s Rule
Background image of page 10
11 According to the Hammond postulate, Path [2] is faster because formation of the carbocation is an endothermic process. Thus, the transition state to form the more stable 2° carbocation is lower in energy. The E a for formation of the more stable 2° carbocation is lower than the E a for formation of the 1° carbocation; the 2° carbocation is formed faster. 3. Hammond Postulate and Markovnikov’s Rule
Background image of page 11

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

View Full DocumentRight Arrow Icon
12 + (1) H Cl Cl H H Cl (95     :     5) + (2) H Br (98     :     2) H Br Br H 3. Markovnikov’s Rule - examples
Background image of page 12
13 Recall that trigonal planar atoms react with reagents from two directions with equal probability. Achiral starting materials yield achiral products.
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 / 62

Chapter08notes - 1. Addition Reactions The characteristic...

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