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Addition to c=c multi bonds
1.
Good Morning to
You All Welcome Dr. V Alex Ramani SJC, Trichy 2
2.
ADDITION TO CARBONCARBON MULTIPLE BONDS Introduction Mechanisms Orientation and Reactivity Examples Dr. V Alex Ramani SJC, Trichy 2
3.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Introduction Two ways of Addition based on the Substrate They are given as follows Dr. V Alex Ramani SJC, Trichy 2
4.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Introduction Four ways of Addition based on the Reagents Three are twostep processes and the fourth one is a onestep process. They are given as follows Dr. V Alex Ramani SJC, Trichy 2
5.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Electrophilic Reagent approaches the double or triple bond substrate to give positive intermediate The positive intermediate is attacked by the nucleophilic species This reaction may be uni , bi or termolecular Let us look at the mechanisms Dr. V Alex Ramani SJC, Trichy 2
6.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Dr. V Alex Ramani SJC, Trichy 2
7.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition The stereochemistry of the addition reaction may be either 'syn' or 'anti' type Mostly openchain intermediates favours 'syn' addition Cyclic intermediate favours more preferentially the 'anti' addition Let us look at these stereochemical aspects Dr. V Alex Ramani SJC, Trichy 2
8.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Dr. V Alex Ramani SJC, Trichy 2
9.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Dr. V Alex Ramani SJC, Trichy 2
10.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Dr. V Alex Ramani SJC, Trichy 2
11.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Year 1911: McKenzie and Fischer independently proved the antiaddition in case of cyclic intermediate formation Addition bromine to maleic acid and fumaric acid to give dlpair and meso forms of 2,3dibromosuccinic acid, respectively Later, chemists proved the formation of 70% of trans isomer when dicarboxyacetylene was brominated Dr. V Alex Ramani SJC, Trichy 2
12.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Dr. V Alex Ramani SJC, Trichy 2
13.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition It has been found that the addition of bromine is not stereospecifically favouring antiaddition product The anti addition depends on the polarity of the solvent Solvent of low dielectric favours 90100% antiaddition Solvent of high dielectric favours nonstereospecific addtion Dr. V Alex Ramani SJC, Trichy 2
14.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Dr. V Alex Ramani SJC, Trichy 2
15.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Electrophilic Addition Dr. V Alex Ramani SJC, Trichy 2
16.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Nucleophilic Addition Nucleophilic Reagent approaches the double or triple bond substrate to give negative intermediate The positive intermediate is attacked by the electrophilic species This addition reaction is favoured when the substrate has an electron withdrawing group Let us look at the mechanisms Dr. V Alex Ramani SJC, Trichy 2
17.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Nucleophilic Addition Dr. V Alex Ramani SJC, Trichy 2 Note: When the substrate contains a good leaving group substitution reaction is more favoured When electronwithdrawing group is present in the substrate, addition reaction is more favoured
18.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Nucleophilic Addition Dr. V Alex Ramani SJC, Trichy 2
19.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Nucleophilic Addition Michael reaction is a type of nucleophilic addition This Michael type of reaction can be reversed by heating either with or without alkali Dr. V Alex Ramani SJC, Trichy 2
20.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Nucleophilic Addition The nucleophilic addition is nonstereospecific and stereoselective The products are formed based on the favourable conformation, assumed by the carbanion Dr. V Alex Ramani SJC, Trichy 2
21.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Nucleophilic Addition The nucleophilic addition of some reagents – EtOD or Me3 CSD to transethyl but2enoate shows anti addition product predominantly Nucleophilic addition to CC triple bond systems mostly yield antiaddition product as that of electrophlic addition Dr. V Alex Ramani SJC, Trichy 2
22.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Free Radical Addition Free Radical addition is a type of chain reaction There are three stages – initiation, propagation and termination of the reaction Dr. V Alex Ramani SJC, Trichy 2
23.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Free Radical Addition Free Radical addition is nonstereospecific But, these reactions are mostly stereoselective. Let us look at some examples Dr. V Alex Ramani SJC, Trichy 2
24.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Free Radical Addition Free Radical addition is becoming stereospecific at low temperature in some cases – The stereospecificity is disappeared at room tempt. – The addition products are 78% d,l and 22% of meso isomes It is due to the formation of bridged intermediate Dr. V Alex Ramani SJC, Trichy 2
25.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Cyclic Mechanisms Some addition reactions go via fourcentre, five centre or sixcenter intermediate mechanisms showing a closed ring intermediate / transition state Dr. V Alex Ramani SJC, Trichy 2
26.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Addition to Conjugated Systems Addition to conjugated double bonded systems shows 1,2addition and 1,4addition The addition reaction goes via openchain or cyclic intermediate Sometimes the reaction is a concerted one Dr. V Alex Ramani SJC, Trichy 2
27.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Addition to Conjugated Systems Let us look at the mechanisms Electrophilic addition via openchain intermediate Dr. V Alex Ramani SJC, Trichy 2
28.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Addition to Conjugated Systems Potential energy diagram of the 1,2 and 1,4addition reactions Dr. V Alex Ramani SJC, Trichy 2
29.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Addition to Conjugated Systems Formation of some uncommon intermediates during the addition mechanism Dr. V Alex Ramani SJC, Trichy 2
30.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Addition to Conjugated Systems Nucleophilic addition to conjugated systems follows the mechanism that resemble the electrophilic addition mechanism Dr. V Alex Ramani SJC, Trichy 2
31.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Addition to Conjugated Systems Freeradical addition to conjugated systems follows the mechanism that resemble the electrophilic addition mechanism Dr. V Alex Ramani SJC, Trichy 2
32.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Reactivity of Addition The reactivity of the substrate towards addition reaction is influenced by the nature of substituent present Dr. V Alex Ramani SJC, Trichy 2
33.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Reactivity of Addition The effect of substituent is so great that there is a generalization as given here. – simple olefines do not react by nucleophilic mechanism, and polyhalo or polycyano olefine do not react by electrophilic mechanism Dr. V Alex Ramani SJC, Trichy 2
34.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Reactivity of Addition The reactivity of the substrate towards electrophilic addition reaction is shown with an example Dr. V Alex Ramani SJC, Trichy 2 Bromination Hydration
35.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Reactivity of Addition The reactivity of alkenic and alkynic substrates have been observed. – The alkenes more preferred to show electrophilic addition and the alkynes show nucleophilic addition more readily Dr. V Alex Ramani SJC, Trichy 2
36.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Reactivity of Addition The reactivity of alkenic and alkynic substrates have been observed. – The Free radical additions can occur in any type of substrate – The nucleophilic radicals behave like nucleophiles and the rate is enhanced in presence of electron withdrawing groups –
The reverse is true for electrophilic radicals – The deciding factor is the presence of a radical initiator(If ) Dr. V Alex Ramani SJC, Trichy 2
37.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Reactivity of Addition The reactivity of alkenic and alkynic substrates have been observed. – Steric influences have profound effect on the reactivity of these multiple bonded substrates Dr. V Alex Ramani SJC, Trichy 2
38.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The orientation of reagents in alkenic and alkynic substrates have been observed. – When unsymmetrical alkenes or alkynes undergo addition, the electrophilic part of the reagent goes to the carbon having more number of hydrogens – This observation was proposed as a rule ~ Markovnikov's rule. This addition takes place favouring the formation of a better stabilised intermediate Dr. V Alex Ramani SJC, Trichy 2
39.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The orientation of reagents in alkenic and alkynic substrates have been observed. – Presence of electron donating substituents in the substrate favours Markovnikov's addition – Presence of electron withdrawing substituents in the substrate favours antiMarkovnikov's addition Dr. V Alex Ramani SJC, Trichy 2
40.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The orientation of reagents in alkenic and alkynic substrates have been observed. – The nucleophilic attack is studied to a very little extent and it is done only in Michael type of addition – Presence of electron withdrawing substituents in the substrate favours nucleophilic attack Dr. V Alex Ramani SJC, Trichy 2
41.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The orientation of reagents in alkenic and alkynic substrates have been observed. – The freeradical attack is influenced very much by the steric factor – The inductive effect has less impact on this reaction Dr. V Alex Ramani SJC, Trichy 2Stability
order of the free radical: 3o > 2o > 1o
42.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The orientation in 5,6 alkenic substrates have been observed to be intramolecular – Cyclic products are preferred and Smaller ring types are more favoured than big rings – It obeying the Baldwin's rule – ExoTrig addition is more preferred than the EndoTrig addition Dr. V Alex Ramani SJC, Trichy 2
43.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The orientation in conjugated alkenic substrates have been observed to be at the tailend part – The attack by the electrophile, nucleophile or free radical will be at the terminal carbon of the conjugated system – It favours the formation of a stable intermediate Dr. V Alex Ramani SJC, Trichy 2
44.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The orientation in allenic substrates have been observed to be at the middle carbon – The attack by the electrophile will be at the middle carbon of the allenic system – It favours the formation of a stable intermediate, though it is an antiMarkovnikov's addition. Dr. V Alex Ramani SJC, Trichy 2
45.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The stereochemistry of orientation – For cyclic compounds, the addition may be syn or anti – In syn addition to unsymmetrical cyclic olefins, the two groups approach from the lesshindered side. Dr. V Alex Ramani SJC, Trichy 2
46.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The stereochemistry of orientation – For cyclic compounds, the addition may be syn or anti for both electrophilic and nucleophilic reagents – In synface addition to unsymmetrical cyclic olefins, the groups approach from the side of electron withdrawing group. –
In antiface addition, the groups approach from the side and opposite of electrondonating group Dr. V Alex Ramani SJC, Trichy 2
47.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Theory of Orientation of Addition The stereochemistry of orientation – The addition of Br2 or HOBr are often anti because of the formation of cyclic intermediate Dr. V Alex Ramani SJC, Trichy 2
48.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Birch Reduction Aromatic rings undergo reduction showing 1,4 addition of hydrogen to give nonconjugated dienes – It follows radical ion mechanism – Electron donating substituents decrease the rate of the reaction. Electron withdrawing groups increase the rate of the reaction. –
The radical ion is proved by the epr studies Dr. V Alex Ramani SJC, Trichy 2
49.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Birch Reduction Aromatic rings undergo reduction showing 1,4 addition of hydrogen to give nonconjugated dienes – Ordinary olefines do not undergo this reduction – Phenylated olefines, internal alkynes and conjugated olefines show this Birch Reduction. –
Benzene shows this reduction to give 1,4diene and not 1,3diene. Dr. V Alex Ramani SJC, Trichy 2
50.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Birch Reduction Aromatic rings undergo reduction showing 1,4 addition of hydrogen to give nonconjugated dienes – Ordinary olefines do not undergo this reduction – Phenylated olefines, internal alkynes and conjugated olefines show this Birch Reduction. –
Benzene shows this reduction to give 1,4diene and not 1,3diene. Dr. V Alex Ramani SJC, Trichy 2
51.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Hydroboration Olefines on hydrobortion give alcohols, ultimately – Borane always goes to carbon having more number of hydrogens. – It follows markovnikov's addition. Boron is more electropositive than hydrogen Dr. V Alex Ramani SJC, Trichy 2
52.
ADDITION TO CARBONCARBON MULTIPLE BONDS..... Hydroboration Olefines on hydrobortion give alcohols, ultimately – Borane BH3 or its substituted derivative – BHR2 attacks the olefinic carbon that is sterically less crowded Dr. V Alex Ramani SJC, Trichy 2
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ADDITION TO CARBONCARBON MULTIPLE BONDS..... Hydroboration Olefines on hydrobortion give alcohols, ultimately – Enantioselective hydroboration using diisopinocampheylborane Dr. V Alex Ramani SJC, Trichy 2
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ADDITION TO CARBONCARBON MULTIPLE BONDS..... Michael Reaction Olefines undergo the following addition – It is a nucleophilic addition – Olefines must have an electron withdrawing group. Otherwise, this reaction is not possible –
The nucleophilic reagent also has the electron withdrawing substituents like COOR, C=O, CN, NO2 , S=O, etc. – The reaction is carried out with malonates, cyanoacetates, acetoacetates, other βketoesters, etc. Dr. V Alex Ramani SJC, Trichy 2
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ADDITION TO CARBONCARBON MULTIPLE BONDS..... Michael Reaction Olefines undergo the following addition – Michael reaction has been carried out traditionally in protic solvents, with catalytic amount of a base. Dr. V Alex Ramani SJC, Trichy 2
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ADDITION TO CARBONCARBON MULTIPLE BONDS..... Michael Reaction Alkynes undergo the following addition – Michael reaction has been shown by some alkynic substrates having an electronwithdrawing group – In some cases, the Michael reaction is possible under acidic conditions Dr. V Alex Ramani SJC, Trichy 2
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