西北农林科技大学：《有机化学 Organic chemistry》课程教学课件（2009）Chapter 06 reactions and mechanisms

Section F REACTIONS AND MECHANISMS >Bond formatiomn >Classification of reactions >Mechanisms

Section F REACTIONS AND MECHANISMS ¾Bond formatiomn ¾Classification of reactions ¾Mechanisms

1 Reactions Bond formation Synthetic organic chemistry is about creating complex molecules from simple starting materials -a process which may involve many different reactions. Designing a synthesis is a bit like chess. a synthetic 'game strategy

1 Reactions Bond formation Bond formation ™Synthetic organic chemistry is about creating complex molecules from simple starting materials - a process which may involve many different reactions. ™Designing a synthesis is a bit like chess. ™ a synthetic 'game strategy

1 Reactions Bond formation Basically,most reactions involve electron- rich molecules forming bonds to electron deficient molecules (i.e.nucleophiles forming bonds to electrophiles). The bond will be formed specifically between the nucleophilic center of the nucleophile and the electrophilic center of the electrophile

1 Reactions Bond formation ™Basically, most reactions involve electron￾rich molecules forming bonds to electron deficient molecules (i.e. nucleophiles forming bonds to electrophiles). ™The bond will be formed specifically between the nucleophilic center of the nucleophile and the electrophilic center of the electrophile

Reactions------Classification Reactions can be classified as acid/base reactions(covered in next section) functional group transformations; one functional group can be converted into another. ▣Normally these reactions are relatively straightforward and proceed in high yield

1 Reactions ------Classification Reactions can be classified as ™acid/base reactions( covered in next section) ™functional group transformations; ‰one functional group can be converted into another. ‰Normally these reactions are relatively straightforward and proceed in high yield

Reaction category/Functional groups Electrophilic addition Alkenes and alkynes Electrophilic Aromatic substitution Nucleophlic addition Aldehydes and ketones Nucleophilic Carboxylic acid derivatives,Alkyl substitution halides Elimination Alcohols and alkyl halides Reduction Alkenes,alkynes,aromatic,aldehydes, ketones,nitriles,carboxylic acids, and carboxylic acid derivatives, Oxidation Alkenes,alcohols,aldehydes Acid/base reactions Carboxylic acids,phenols,amines

Reaction category/ Functional groups Electrophilic addition Alkenes and alkynes Electrophilic substitution Aromatic Nucleophlic addition Aldehydes and ketones Nucleophilic substitution Carboxylic acid derivatives, Alkyl halides Elimination Alcohols and alkyl halides Reduction Alkenes,alkynes, aromatic, aldehydes, ketones, nitriles, carboxylic acids, and carboxylic acid derivatives, Oxidation Alkenes, alcohols, aldehydes Acid/base reactions Carboxylic acids, phenols, amines

Examples Alkenes C=C Alkynes C三C Aromatic CoH6 0 Aldehydes and ketones C=O Alkyl halides RX

Examples ™Alkenes C=C ™Alkynes C三C ™Aromatic C6H6 ™Aldehydes and ketones C=O ™Alkyl halides RX

Addition X-Y Elimination + :Br: :Br: :Br Br: C=C An alkene :Br: ●。 A bromonium ion Br HBr Alkene Productlike transition state Carbocation

1.5 bonds on average H H 2007 Thomson Higher Education M 移 Naphthalene

Br-Br+FeBr3 Br+-FeBr4 Slow 1An electron pair from the benzene ring attacks the positively polarized bromine,forming a new C-Br bond Br FeBr4 and leaving a nonaromatic carbocation intermediate. 2A base removes H+from the carbocation intermediate, and the neutral substitution product forms as two electrons from the C-H bond move to re-form the aromatic ring. Fast Br +HBr FeBr3

R-X Nu:- R一Nu+X: Nu:-+c-x Tetrahedral The SN2 Reaction Planar Nu-C Tetrahedral

The S N 2 Reaction