{"id":1611,"date":"2018-11-29T21:27:16","date_gmt":"2018-11-29T21:27:16","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/?post_type=chapter&p=1611"},"modified":"2019-01-09T05:27:13","modified_gmt":"2019-01-09T05:27:13","slug":"20-7-conjugate-addition","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/chapter\/20-7-conjugate-addition\/","title":{"raw":"20.7 Conjugate addition","rendered":"20.7 Conjugate addition"},"content":{"raw":"
<\/header>
\r\n

One of the largest and most diverse classes of reactions is composed of nucleophilic additions to a carbonyl group. Conjugation of a double bond to a carbonyl group transmits the electrophilic character of the carbonyl carbon to the beta-carbon of the double bond. These conjugated carbonyl are called enones or \u03b1, \u03b2 unsaturated carbonyls. A resonance description of this transmission is shown below.<\/p>\r\n\"http:\/\/www2.chemistry.msu.edu\/faculty\/reusch\/VirtTxtJml\/Images2\/enoneres.gif\"\r\n\r\nFrom this formula it should be clear that nucleophiles may attack either at the carbonyl carbon, as for any aldehyde, ketone or carboxylic acid derivative, or at the beta-carbon. These two modes of reaction are referred to as 1,2-addition and 1,4-addition respectively. A 1,4-addition is also called a conjugate addition.\r\n

\r\n

Basic reaction of 1,2 addition<\/h2>\r\nHere the nucleophile adds to the carbon which is in the one position. The hydrogen adds to the oxygen which is in the two position.\r\n\r\n\"2.jpg\"\r\n\r\n<\/div>\r\n
\r\n

Basic reaction of 1,4 addition<\/h2>\r\n\"3.jpg\"\r\n\r\nIn 1,4 addition the nucleophile is added to the carbon \u03b2 to the carbonyl while the hydrogen is added to the carbon \u03b1 to the carbonyl.\r\n
\r\n

Mechanism for 1,4 addition<\/h3>\r\n1) Nucleophilic attack on the carbon \u03b2 to the carbonyl\r\n\r\n\"4.jpg\"\r\n\r\n2) Proton Transfer\r\n\r\n\"5.jpg\"\r\n\r\nHere we can see why this addition is called 1,4. The nucleophile bonds to the carbon in the one position and the hydrogen adds to the oxygen in the four position.\r\n\r\n3) Tautomerization\r\n\r\n\"6.jpg\"\r\n\r\nGoing from reactant to products simplified\r\n\r\n\"7.jpg\"\r\n\r\n<\/div>\r\n<\/div>\r\n
\r\n

1,2 vs. 1,4 addition<\/h2>\r\nWhether 1,2 or 1,4-addition occurs depends on multiple variables but mostly it is determined by the nature of the nucleophile. During the addition of a nucleophile there is a competition between 1,2 and 1,4 addition products. If the nucleophile is a strong nucleophile, such as a Grignard reagent<\/a>, both the 1,2 and 1,4 reactions are irreversible and therefore are under kinetic control. Since 1,2-additions to the carbonyl group are fast, we would expect to find a predominance of 1,2-products from these reactions.\r\n\r\nIf the nucleophile is a weak base, such as alcohols or amines, then the 1,2 addition is usually reversible. This means the competition between 1,2 and 1,4 addition is under thermodynamic control. In this case 1,4-addition dominates because the stable carbonyl group is retained.\r\n\r\n<\/div>\r\n
\r\n

Nucleophiles which add 1,4 to \u03b1,\u03b2 unsaturated carbonyls<\/h2>\r\nWater\r\n\r\n\"8.jpg\"\r\n\r\nAlcohols\r\n\r\n\"9.jpg\"\r\n\r\nThiols\r\n\r\n\"10.jpg\"\r\n\r\n1o<\/sup> Amines\r\n\r\n\"11.jpg\"\r\n\r\n2o<\/sup> Amines\r\n\r\n\"12.jpg\"\r\n\r\nHBr\r\n\r\n\"13.jpg\"\r\n\r\nCyanides\r\n\r\n\"14.jpg\"\r\n\r\n<\/div>\r\n
\r\n\r\n \r\n

Gilman Reagents: These act as a source of R:-<\/sup><\/p>\r\n\"15.jpg\"\r\n\r\nExample\r\n\r\n\"16.jpg\"\r\n\r\n<\/div>\r\n

\r\n

Nucleophiles which add 1,2 to \u03b1, \u03b2 unsaturated carbonyls<\/h2>\r\nMetal Hydrides\r\n\r\n\"17.jpg\"\r\n\r\n\"18.jpg\"\r\n\r\nGrignard Reagents\r\n\r\n\"19.jpg\"\r\n\r\nOrganolithium Reagents\r\n\r\n\"20.jpg\"\r\n\r\n<\/div>\r\n
\r\n

Contributors<\/h3>\r\nProf. Steven Farmer (Sonoma State University<\/a>)\r\n\r\nWilliam Reusch, Professor Emeritus (Michigan State U.<\/a>), Virtual Textbook of\u00a0Organic\u00a0Chemistry<\/a>\r\n\r\n
<\/header>
\r\n
\r\n
\r\n
\r\n

Exercise<\/h3>\r\n

Indicate whether the following nucleophiles are more likely to undergo 1,2-addition or 1,4-addition.<\/span><\/p>\r\n

\"\"<\/span><\/a><\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n

\r\n\r\n \r\n\r\n<\/div>\r\n<\/section><\/div>\r\n<\/section>","rendered":"
<\/header>\n
\n

One of the largest and most diverse classes of reactions is composed of nucleophilic additions to a carbonyl group. Conjugation of a double bond to a carbonyl group transmits the electrophilic character of the carbonyl carbon to the beta-carbon of the double bond. These conjugated carbonyl are called enones or \u03b1, \u03b2 unsaturated carbonyls. A resonance description of this transmission is shown below.<\/p>\n

\"http:\/\/www2.chemistry.msu.edu\/faculty\/reusch\/VirtTxtJml\/Images2\/enoneres.gif\"<\/p>\n

From this formula it should be clear that nucleophiles may attack either at the carbonyl carbon, as for any aldehyde, ketone or carboxylic acid derivative, or at the beta-carbon. These two modes of reaction are referred to as 1,2-addition and 1,4-addition respectively. A 1,4-addition is also called a conjugate addition.<\/p>\n

\n

Basic reaction of 1,2 addition<\/h2>\n

Here the nucleophile adds to the carbon which is in the one position. The hydrogen adds to the oxygen which is in the two position.<\/p>\n

\"2.jpg\"<\/p>\n<\/div>\n

\n

Basic reaction of 1,4 addition<\/h2>\n

\"3.jpg\"<\/p>\n

In 1,4 addition the nucleophile is added to the carbon \u03b2 to the carbonyl while the hydrogen is added to the carbon \u03b1 to the carbonyl.<\/p>\n

\n

Mechanism for 1,4 addition<\/h3>\n

1) Nucleophilic attack on the carbon \u03b2 to the carbonyl<\/p>\n

\"4.jpg\"<\/p>\n

2) Proton Transfer<\/p>\n

\"5.jpg\"<\/p>\n

Here we can see why this addition is called 1,4. The nucleophile bonds to the carbon in the one position and the hydrogen adds to the oxygen in the four position.<\/p>\n

3) Tautomerization<\/p>\n

\"6.jpg\"<\/p>\n

Going from reactant to products simplified<\/p>\n

\"7.jpg\"<\/p>\n<\/div>\n<\/div>\n

\n

1,2 vs. 1,4 addition<\/h2>\n

Whether 1,2 or 1,4-addition occurs depends on multiple variables but mostly it is determined by the nature of the nucleophile. During the addition of a nucleophile there is a competition between 1,2 and 1,4 addition products. If the nucleophile is a strong nucleophile, such as a Grignard reagent<\/a>, both the 1,2 and 1,4 reactions are irreversible and therefore are under kinetic control. Since 1,2-additions to the carbonyl group are fast, we would expect to find a predominance of 1,2-products from these reactions.<\/p>\n

If the nucleophile is a weak base, such as alcohols or amines, then the 1,2 addition is usually reversible. This means the competition between 1,2 and 1,4 addition is under thermodynamic control. In this case 1,4-addition dominates because the stable carbonyl group is retained.<\/p>\n<\/div>\n

\n

Nucleophiles which add 1,4 to \u03b1,\u03b2 unsaturated carbonyls<\/h2>\n

Water<\/p>\n

\"8.jpg\"<\/p>\n

Alcohols<\/p>\n

\"9.jpg\"<\/p>\n

Thiols<\/p>\n

\"10.jpg\"<\/p>\n

1o<\/sup> Amines<\/p>\n

\"11.jpg\"<\/p>\n

2o<\/sup> Amines<\/p>\n

\"12.jpg\"<\/p>\n

HBr<\/p>\n

\"13.jpg\"<\/p>\n

Cyanides<\/p>\n

\"14.jpg\"<\/p>\n<\/div>\n

\n

 <\/p>\n

Gilman Reagents: These act as a source of R:–<\/sup><\/p>\n

\"15.jpg\"<\/p>\n

Example<\/p>\n

\"16.jpg\"<\/p>\n<\/div>\n

\n

Nucleophiles which add 1,2 to \u03b1, \u03b2 unsaturated carbonyls<\/h2>\n

Metal Hydrides<\/p>\n

\"17.jpg\"<\/p>\n

\"18.jpg\"<\/p>\n

Grignard Reagents<\/p>\n

\"19.jpg\"<\/p>\n

Organolithium Reagents<\/p>\n

\"20.jpg\"<\/p>\n<\/div>\n

\n

Contributors<\/h3>\n

Prof. Steven Farmer (Sonoma State University<\/a>)<\/p>\n

William Reusch, Professor Emeritus (Michigan State U.<\/a>), Virtual Textbook of\u00a0Organic\u00a0Chemistry<\/a><\/p>\n

<\/header>\n
\n
\n
\n
\n

Exercise<\/h3>\n

Indicate whether the following nucleophiles are more likely to undergo 1,2-addition or 1,4-addition.<\/span><\/p>\n

\"\"<\/span><\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n

\n

 <\/p>\n<\/div>\n<\/section>\n<\/div>\n<\/section>\n\n\t\t\t

\n\t\t\t

Candela Citations<\/h3>\n\t\t\t\t\t
\n\t\t\t\t\t\t
\n\t\t\t\t\t\t\t
CC licensed content, Shared previously<\/div>