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Organic Compounds Containing Halogens Class 11 Notes Chemistry

Organic Compounds Containing Halogens can be divided into two groups:

  • Alkyl Halides: Aliphatic carbon chain with halogen atom(s) as substitution.. Example: Chlorobutane. 
  • Aryl Halides: Aromatic carbon ring with halogen atom(s) as substitution on ring. Example: Chlorobenzene.

Methods of Preparation of Alkyl Halides:
(a) Grove’s process: Replacement of “OH” group in primary and secondary alcohols with an “X’ atom in presence of Zinc chloride.
Organic Compounds Containing Halogens Class 11 Notes Chemistry
The reaction follows SN2 mechanism when the concentration of zinc chloride is low.
(b) Darzen Process: Reaction of thionyl chloride with straight-chain primary alcohols without  presence or absence of pyridine.
In presence of pyridine:
ROH + SOCl→ HCl + ROSOCl
HCl+C5H5N →C5H5NH++Cl-
ROSOCl + Cl →RCl + SO   (SN2)

  • Action of a phosphorus halide on the alcohol: ROH + PCl5 →  RCl + HCl + POCl3.
  • By addition of Halogen to an alefins: R-CH=CH2 +Br2+CCl4  →R-CH(Br)CH2Br 
  • Photohalogenation: CH4 + Cl+hv → CH3Cl + HCl
  • Displacement of one halogen atom by another:RCl + NaI →RI + NaCl
  • Bonodine – Hünsdiecker Reaction: RCO2Ag + Br2→RBr + CO2 + AgBr
  • Hydrohalogenation of unsaturated hydrocarbons:
    • In absence of peroxide: RCH=CH2 +HBr→RCH(Br)CH3
    • In presence of peroxide: RCH=CH2 +HBr + Peroxide →RCH2CH2Br

Methods of Preparation of aryl halides

  • Halogenation:  Ar-H + X2 +Lewis Base → Ar-x + HX
  • From diazonium salts:
    • C6H5N2Cl + HBF4 →C6H5F               (Schiemann Reaction)
    • C6H5N2Cl + CuCl →C6H5Cl              (Sandmeyer Reaction)
    • C6H5N2Cl + Cu powder →C6H5Cl      (Gatterman Reaction)

SN1 and SN2 mechanism:

 
SN1
SN2
 
Steps
Two :  
(1) R:Xl → R+ + X-
 (2) R+ + Nu- l →RNu
One :
R:X + Nu- l → RNu + X-
 
TS of slow step
Organic Compounds Containing Halogens Class 11 Notes Chemistry
Organic Compounds Containing Halogens Class 11 Notes Chemistry
Rate
            =K [RX] (1st order)
=K[RX] [:Nu-] (2nd order)
Stereochemistry
Inversion and racemization
Inversion (backside attack)
Molecularity
Unimolecular
Bimolecular
Reactivity
structure of R
Determining Factor
Nature of X
Solvent effect on rate
3o> 2o> 1o> CH3
Stability of R+
RI> RBr> RCl> RF
Rate increases in polar solvent
CH3> 1o> 2o> 3o
Steric hindrance in R group
RI> RBr> RCl> RF
with Nu- there is a large rate increase in polar aprotic solvents.
Effect of nucleophile
No effect as it does not appear in the rate expression.
Rate depends on nucleophilicity
I-  > Br-  > Cl- ; RS-  > RO-
Catalysis
Lewis acid, eg. Ag+, AlCl3, ZnCl2
None
Competitive reaction
Elimination, rearrangement
Elimination


Reactions of Alkyl Halides:

  • Hydrolysis: : RX  + OH → ROH  +  X
  • Williamson Synthasis: R-ONa +R'X → R-R' + NaX
  • Reaction with dry silver oxide: 2R-X + Ag2O → R-O-R
  • Reaction with sodio-Alkynides: R-C≡C-Na +X-R→ R-C=C-R +NaX
  • Reaction with potassium-cyanide: KCN+X-R→ RCN +KX
  • Reaction with silver-cyanide: AgCN+X-R→ RNC +AgX
  • Reaction with silver-nitrite: AgNO2+X-R→ RNO2 +AgX
  • Reaction with potassium-nitrite: KNO2+X-R→ R-O-N=O +KX
  • Fridal Craft Reaction: R-X + C6H6 + AlCl3→C6H5-R
  • Malonic Ester Synthasis: R-X + -CH(CO2C2H5)→R-CH(CO2C2H5)2  +HX
  • Acetoacetic Ester Synthasis: R-X + -CH(CO2CH3)2 →R-CH(CO2CH3)2 +HX
  • Reaction with Ammonia: R-X +NH3→ R-NH2 +HX
  • Wurtz Reaction: 2R-I+ 2Na →R—R + 2NaI
  • Dehydrohalogenation: CH3.CH2.CH2Br + alco.KOH → CH3–CH = CH+ KBr + H2O 
  • Reaction with alcoholic AgNO3:  R-X +AgNO3 → R+ + AgX↓+HNO

Substitution Versus Elimination:

CH3X

Methyl

  • RCH2X - 1o
  • R2CHX - 2o
  • R3CX - 3o

Bimolecular reactions only

  • R3CX - SN1/E1 or E2

Gives SN2 reactions

  • RCH2X - Gives mainly SN2 except with a hindered strong base [e.g., (CH3)3CO] and then gives mainly E2.
  • R2CHX - Gives mainly SN2 with weak bases (e.g., I, CN, RCO2) and mainly E2 with strong bases (e.g., RO)
  • R3CX - No SN2 reaction. In solvolysis gives SN1/E1, and at lower temperature S­N1 is favoured. When a strong base (e.g., RO) is used. E2 predominates.

Haloform(Tri halide):

  • Preparation: It can be prepared from any alcohol having –CH(OH)CH3 group or from the aldehydes and ketones formed from above type of alcohols i.e, from a carbonyl compound having three a - hydrogen atoms by the action of X2 and an alkali or Na2CO3.
  • Laboratory Preparation of CHCl3:
    Organic Compounds Containing Halogens Class 11 Notes Chemistry
  • Physical properties of CHCl3: colour less liquid with sweet smell and test. It is heavier  than water and insoluble in it but soluble in alcohol and ether.

Chemical Reactions of CHCl3:

  • Oxidation: CHCl+ 1/2 O2 → HCl + COCl2 (phosgene)
  • Hydrolysis: CHCl3 + 4NaOH → HCOONa + 3NaCl + 2H2O
  • Carbyl amine reactions: CHCl3 + CH3NH+ 3NaOH →CH3N≡C +3NaCl +3H2O
The document Organic Compounds Containing Halogens Class 11 Notes Chemistry is a part of the NEET Course NCERT Exemplar & Revision Notes for NEET.
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FAQs on Organic Compounds Containing Halogens Class 11 Notes Chemistry

1. What are halogens in organic compounds?
Ans. Halogens are a group of chemical elements that include fluorine, chlorine, bromine, iodine, and astatine. When these elements are incorporated into organic compounds, they form organic compounds containing halogens.
2. What are some examples of organic compounds containing halogens?
Ans. Examples of organic compounds containing halogens include chloroform (CHCl3), bromobenzene (C6H5Br), iodomethane (CH3I), and fluoroacetic acid (CH2FCOOH).
3. How do halogens affect the properties of organic compounds?
Ans. Halogens can significantly impact the properties of organic compounds. For example, the presence of halogens can increase the boiling points and melting points of organic compounds. Halogens also play a role in determining the reactivity and stability of organic compounds.
4. What are the applications of organic compounds containing halogens?
Ans. Organic compounds containing halogens have various applications in different industries. For instance, chlorofluorocarbons (CFCs) were widely used as refrigerants and aerosol propellants before their harmful environmental effects were discovered. Halogenated solvents are commonly used in cleaning processes, and halogenated flame retardants are used to reduce the flammability of materials.
5. Are organic compounds containing halogens harmful to the environment?
Ans. Some organic compounds containing halogens can be harmful to the environment. For example, certain chlorinated organic compounds are known to be persistent and bioaccumulative, meaning they can accumulate in the environment and in the food chain. These compounds can have detrimental effects on ecosystems and human health. However, not all organic compounds containing halogens are harmful, and their environmental impact depends on their specific chemical structure and usage.
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