1 Some Important Reactions of Alcohols 1. Dehydration = loss of H 2 O to form an alkene 2. Oxidation = loss of H to form a C=O compound

2 Dehydration Examples CH 3 CHCH 3 CH 2 =CHCH 3 + H 2 O OH 2-propanol --> propene + water general pattern: alcohol --> alkene + water

3 H H OH H Another example H 2 O + cyclopentanol --> cyclopentene + water

4 How does reaction occur? * Loss of water from alcohol alone has high activation energy = alcohols dehydrate very, very, very slowly by themselves * speed up reaction by lowering E act with catalyst

5 Catalyst for dehydration of alcohol is usually acid = H + from H 2 SO 4 (sulfuric acid) or enzyme in living organism.

6 Main thing to focus on: C-C O H HO HH H H+H+ + lose H + & H 2 O C=C alkene C=C forms between C bonded to OH and adjacent C bonded to H lost as H +

7 When the C-O bonds breaks to lose H 2 O, an adjacent C-H bond breaks to lose H +. The result is formation of the new pi (  ) bond to make the alkene. Catalyst helps OH leave as H 2 O from alcohol.

8 When there is more than one kind of H on the C next to C-OH, more than one alkene can form: CH 3 CHCH 2 CH 3 H 2 O + OH H+H+ heat CH 2 =CHCH 2 CH 3 + CH 3 CH=CHCH 3

9 Oxidation Reaction Examples CH 3 CH 2 -CH-CH 3 OH [O] CH 3 CH 2 -C-CH 3 O 2° alcohol ketone oxidizing agent

10 General reaction: R-CH-R’ R-C-R’ OH O [O] 2° ROH + [O] ---> ketone

11 Oxidizing agents remove H and e - from the grouping H-C-O-H that makes up the alcohol group to form C=O. Many reagents can do this: common ones are Cr or Mn compounds. Even household bleach (NaOCl) can be [O].

12 Primary alcohols can be oxidized in 2 stages: R-CH 2 -OH R-C-H O [O] aldehyde R-C-H O [O] R-C-OH O carboxylic acid

13 Aldehydes are easier to oxidize than 1° alcohols, so it is sometimes difficult to stop the reaction at the aldehyde stage. Special reagents have been developed to make it possible to get aldehydes by oxidizing a 1° alcohol.

14 Tertiary alcohols are not oxidized because there is no H on the C bonded to OH: R-C-O-H is 3° alcohol R R CH 3 -C-O-H CH 3 no H on C

15 Phenols are benzene compounds with an OH group attached to a sp 2 C in ring: OH “phenol” salicylic acid OH CO 2 H

16 Phenols & Alcohols are not alike! * both have C-O-H * both form H-bonds, BUT: * alcohols are neutral compounds * phenols are acidic

17 ETHERS have the general formula R-O-R’ (has C-O-C bond) *bond angles about 109° *tetrahedral e - pairs on O *C-O-C shape is angular or bent

18 CH 3 CH 2 -O-CH 2 CH 3 “diethyl ether” is symmetrical CH 3 -O-CH 2 CH 2 CH 3 “methyl propyl ether” is unsymmetrical both Alkyl groups can be the same or different:

19 non-IUPAC names for ethers = “common names” name of alkyl group 1 name of alkyl group 2 ether name of alkyl group 1 (space) name of alkyl group 2 (space) ether see previous slide for examples

20 Ethers do not provide a H for a hydrogen bond, but can provide the electron pair of O. So: ethers are H-bond acceptors, they donate :O: to the H of another O-H or H-N

21 R R O ether H-bond acceptor H-O R’ alcohol H-bond donor

22 Sulfur Analogs of Alcohols and Ethers R-S-Hthiol or mercaptan R-S-R’thioether R-S-S-R’disulfide Simply be able to recognize the type from structure.