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Carbon Bond Heterolysis: Understanding Carbocations and Carbanions, Quizzes of Organic Chemistry

University of Southern Mississippi (USM)Organic Chemistry

The concept of heterolytic bond cleavage in carbon compounds and the formation of carbocations and carbanions. It covers formal charges, reactivity as electrophiles and nucleophiles, and the curved arrow formalism. Students will learn how to identify electrophiles, nucleophiles, lewis acids, and lewis bases in reactions.

Typology: Quizzes

Pre 2010

Uploaded on 08/19/2009

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Carbon Bond Heterol

sis Processes:

Carbocations and Carbanions

When a bond to carbon is broken heterolytically, the carbon may

carry either a positive (carbocation) or negative (carbanion) charge.

Modes of Heterolytic Bond Cleavage

C:X

δ+ δ

−

++ X:

a carbocation

δ− -+ Y

a carbanion

C:Y C:

Partial preview of the text

Download Carbon Bond Heterolysis: Understanding Carbocations and Carbanions and more Quizzes Organic Chemistry in PDF only on Docsity!

Carbon Bond Heterolysis Processes:Carbocations and Carbanions

When a bond to carbon is broken heterolytically, the carbon maycarry either a positive (carbocation) or negative (carbanion) charge.Modes of Heterolytic Bond Cleavage

C:X

δ+

δ−

+^

X:

a carbocation

C

δ+ δ−

-^

+^

+Y

a carbanion

C:Y

C:

Formal Charges

Carbocations have only six electrons in the valence or bonding level andare electron-deficient. The charge on carbon can be determined by asimple calculationStep One: Determine how many of the valence electronsFor each pair of bonding electrons, one "belongs" to carbon.All nonbonding electrons in the valence level "belong" to carbon.

"belong" to carbon.+

a carbocation

In a carbocation, only

of the 6 bonding

electrons "belong" to the carbon. Thereare no nonbonding electrons.

C

The Reactivity of Chemical IntermediatesCarbocations as Electrophiles

Since carbocations are electron-deficient in the valence level, they arestrong Lewis acids. Carbocations react rapidly with Lewis bases,species that are capable of donating electrons. Carbocations are calledelectrophiles

a carbocation(an electrophile)

+^

:B

C

An Example

+^

C^

O H

H

Lewis Base

O H

H

H C

H

O

H

H C

H

an alcohol

-H

C B

Carbanions as Nucleophiles

Carbanions are Lewis bases. They donate an electron pair to Lewisacids such as H

+^ and other electropositive atoms and groups.

Carbanions are called nucleophiles

C

carbanion (a nucleophile)

+^

δ+ δ−H-ALewis acid

A

C

H +

C

L

C

carbanion (a nucleophile)

Lewis acid

L

C

C^

+^

Quiz Chapter 3 Section 4In the reaction below, use the curved arrow formalism to showmovement of an electron pair.C

H 6

CH 5

OH 3

: :

H 6

CH 5

-OCH 2

electrophile Identify the electrophile and nucleophile in the reaction.Identify the Lewis acid and Lewis base in the reaction.

nucleophile

Lewis acid

Lewis base

Carbon Bond Heterolysis: Understanding Carbocations and Carbanions, Quizzes of Organic Chemistry

Related documents

Partial preview of the text

Download Carbon Bond Heterolysis: Understanding Carbocations and Carbanions and more Quizzes Organic Chemistry in PDF only on Docsity!

Carbon Bond Heterolysis Processes:Carbocations and Carbanions

When a bond to carbon is broken heterolytically, the carbon maycarry either a positive (carbocation) or negative (carbanion) charge.Modes of Heterolytic Bond Cleavage

C:X

+^

+^

X:

C

-^

+^

+Y

C:Y

C:

Formal Charges

"belong" to carbon.+

C

The Reactivity of Chemical IntermediatesCarbocations as Electrophiles

+^

:B

C

An Example

+^

C^

O H

H

O H

H

H C

H

H

O

H

H C

H

H

-H

Carbanions as Nucleophiles

Carbanions are Lewis bases. They donate an electron pair to Lewisacids such as H

+^ and other electropositive atoms and groups.

Carbanions are called nucleophiles

C

+^

δ+ δ−H-ALewis acid

A

C

H +

C

L

C

L

C

C^

+^