IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

mk_suhas

Greetings to my dear Goiitians,

Few doubts in Organic Chemistry has been bothering me for quite some days. I don't go for any coaching institutions. Hence, this was the only place where I could put up my doubts. I hope, my doubts get clarified soon.

Note: I have used reagents within {} which are supposed to be represented on top of arrows.

1. Friedel Craft's Reaction.

CH₂=CH₂ + C(CH3)₃-Cl {AlCl₃}

C(CH₃)₃-CH₂-CH₂-Cl

The following mechanism involves formation of carbocation.

C(CH₃)₃-Cl {AlCl₃ , -AlCl₄^-}

C⁺(CH₃)₃ {CH₂=CH₂}

C(CH₃)₃-CH₂-CH₂⁺ {AlCl₄^-}

C(CH₃)₃-CH₂-CH₂Cl

This is what my book says.

But due to the formation of carbocation, there's a possibility of undergoing HYDRIDE SHIFT for greater stability of the molecule.

Due to the Hydride shift we get the molecule, C(CH₃)₃-CHCl-CH₂

But there should be a single solution naaa...
Is the book wrong? Or am i?

2. Grignard's Reagent

1-Bromo,3-Chloro Cyclobutane {Mg/ether}

???

3. Alkyne + Na/liquid NH_3.

RC=CR {Na/liquid NH₃}

R-HC=CH-R [trans-alkene]

And, HC

CH {Na/liquid NH₃}

HC

C^-Na⁺ {R-X}

HC

CR

Does the reagent [Na/liquid NH₃] behave differently for different alkynes? i.e. does it follow substitution reaction for terminal alkyne and addition reaction for other alkynes? If so, then what would be the product for

RC

CH {Na/liquid NH₃}

???

I appreciate if someone justifies his/her answer(s).

Thank You in advance.

harsha_27

1.why are u getting a doubt here........a reaction

may have one or more than one (most probably)

products......practically almost all rxns in organic

involves one or more than one products....the major

product is what we discuss about....

2.here carbon containing Bromine is attacked and

grignard reagent is formed.

3. Na/liq.NH3 is a reducing agent .......giving trans

addition of hydrogen at unsaturated carbon sites

.....i think 2nd reaction is wrong.....Na/liqNH3

reduces the triple bond....

RCCH ------{Na/liq.NH3}--->RCH2CH3

mk_suhas

Can you please justify your answer for question 2?

Coming to problem 3,
1st reaction has been described in the chapter alkene, 2nd has been described in the chapter alkyne.
And for RCCH, i think it should be a alkene RCHCH2

harsha_27

2.b'coz Bromine is larger in size and is a good leaving group than chlorine ......got it??

3.yeah........that will form if u use i equivalent of reagent ..... upon complete reduction RCH2CH3 is formed.......ok

mk_suhas

Noway of complete reduction...
Na/liquid NH3 is used for partial reduction like Lindlar's Catalyst.

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