Alkyl Halides & Alcohols

Salman Bin Abdulaziz University
College of Applied Medical Science,
Medical lab science Department
Organic Chemistry: CHEM-106,
2nd semester, 2nd level.

Alcohols (R-OH), and Alkyl Halides,R-X(X = F, Cl, Br or I)

Alkyl halides can be prepared viasubstitutionreactions:

  • Radical halogentaion of alkanes R-H + X2R-X + HX
  • Reaction of alcohols with hydrogen halides, R-OH + HXR-X + H2O
  • Reaction of alcohols with reagents such as SOCl2, PCl3, PBr3

Functional Groups

  • Afunctional groupis an atom or a group of atoms within a molecule (e.g. -Cl or -CO2H) which define reactivitywrite.
  • Functional groupsdefine reactivity

What is a reaction ?

  • A reaction is the process by which one compound is transformed into a new compound,e.g.write.

ALCOHOLS

Nomenclature:

Functional group suffix =-ol
Functional group prefix =hydroxy-

Nomenclature / Formula
Functional class name =alkyl alcohole.g.ethyl alcohol
Substituent suffix = -ole.g.ethanol
Substituent prefix =hydroxy-e.g.hydroxyethane
Structural unit : alcohols contain R-OH /
  • The root name is based on the longest chain with the -OH attached.
  • The chain is numbered so as to give the alcohol unit the lowest possible number.
  • The alcohol suffix is appended after the hydrocarbon suffix minus the "e" :e.g. -ane + -ol = -anol or -ene + ol = -enol.

  • Functional group is an alcohol, therefore suffix = -ol
  • Hydrocarbon structure is an alkane therefore-ane
  • The longest continuous chain is C3 therefore root =prop
  • It doesn't matter which end we number from, the alcohol group locant is2-
propan-2-olor 2-propanol
(orisopropanol) /
CH3CH(OH)CH3
  • Functional group is an alcohol, therefore suffix = -ol
  • Hydrocarbon structure is an alkene therefore -ene
  • The longest continuous chain is C4 therefore root =but
  • The first point of difference rule requires numbering from therightas drawn to make the alcohol group locant1-
  • Hence the alkene locant is3-
but-3-en-1-olor 3-buten-1-ol / 14CH2=23CH32CH241CH2OH

Types of Alcohols:

  1. PRIMARY,
  2. SECONDARY
  3. TERTIARY

Alcohols are described as primary (1o), secondary (2o) or tertiary (3o) depending on how many alkyl substiutents are attached to the C-OH unit.

ethanol / 2-propanol / t-butanol
2-methyl-2-propanol
1o / 2o / 3o

Check by counting the number of C atoms attached to the C with the O attached.

Physical Properties:

  • The polar nature of the O-H bond (due to the electronegativity difference of the atoms ) results in the formation of hydrogen bonds with other alcohol molecules or other H-bonding systems (e.g. water).
  • Therefore due to this reason:
  • high melting and boiling points compared to analogous alkanes
  • high solubility in aqueous media

Synthesis of Alcohol

1.from a Ketone

3o

2.Reduction

Synthesis of Alcohol from an Aldehyde
3.Synthesis from a Carboxylic Acid

Alkyl halide formation

Alcohols are converted to alkyl halides by Nucleophilic Substitution reactions with halogen acids.

ALKYL HALIDES

Nomenclature:
Functional group suffix =-halide
Functional group prefix =halo-

Haloalkanes / Alkyl halides

Haloalkanes are named by adding a prefix to the name of the alkane from which they are derived. The prefix denotes the particular halogen used.

F=Fluoro-
Cl=Chloro-
Br=Bromo-
I=Iodo-

If other substituents need to be named, all prefixes are still put in alphabetical order. When necessary, numbers identify substituent locations.

Example names of haloalkanes

IUPAC name / Common name
CH3—F / Fluoromethane / Methyl fluoride
CH3—Cl / Chloromethane / Methyl chloride
CH3—Br / Bromomethane / Methyl bromide
CH3—I / Iodomethane / Methyliodide
Nomenclature / Formula
Functional group suffix =halide(i.e. fluoride, chloride, bromide, iodide)
Substituent name =halo-(i.e. fluoro, chloro, bromo, iodo)
Structural unit :haloalkanes contain R-X where X = F, Cl, Br, Ietc.
Notes:
  • Haloalkanes can also be named as alkyl halides despite the fact that the halogens are higher priority than alkanes.
  • The alkyl halide nomenclature is most common when the alkyl group is simple.
/

Haloalkane style:

The root name is based on the longest chain containing the halogen.

  • This root give the alkane part of the name.
  • The type of halogen defines the halo prefix,e.g.chloro-
  • The chain is numbered so as to give the halogen the lowest possible number

Alkyl halide style:

The root name is based on the longest chain containing the halogen.

  • This root give the alkyl part of the name.
  • The type of halogen defines the halide suffix,e.g.chloride
  • The chain is numbered so as to give the halogen the lowest possible number.

Haloalkane style:
  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C3 therefore root =prop
  • The substituent is a chlorine, therefore prefix =chloro
  • The first point of difference rule requires numbering from therightas drawn, the substituent locant is1-
1-chloropropane /
CH3CH2CH2Cl
Alkyl halide style:
  • The alkyl group is C4, it's atert-butyl
  • The halogen is a bromine, therefore suffix =bromide
tert-butyl bromide
Haloalkane style:
  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C3 therefore root =prop
  • The substituent is a bromine, therefore prefix =bromo
  • There is a C1 substituent =methyl
  • The substituent locants are both2-
2-bromo-2-methylpropane / (CH3)3CBr

Primary, secondary or tertiary ? In a similar fashion to alcohols, alkyl halides are described as primary (1o), secondary (2o) or tertiary (3o) depending on how many alkyl substituents are attached to the C-X unit.

chloromethane
or
methyl chloride / bromoethane
or
ethyl bromide / 2-bromopropane
or
isopropyl bromide / 2-bromo-2-methylpropane
or
tert-butyl bromide
primary / secondary / tertiary

Physical Properties:

  • The polar bond creates a molecular dipole that raises the melting points and boiling points compared to alkanes.

Reactivity:

  • The halogens (Cl, Br and I) aregood leaving groups.
  • The polarity makes the C atom electrophilic and prone to attack by nucleophiles

NUCLEOPHILIC SUBSTITUTION REACTIONS

Nucleophilic substitution reactions are an important class of reactions that allow the interconversion of functional groups, for exampleR-OHR-Br.

What is "nucleophilic substitution"?

Anucleophileis an theelectron rich species that will react with an electron poor species.

Asubstitutionimplies that one group replaces another

What are Carbocations?

Stability:
The general stability order of simple alkyl carbocations is: (most stable) 3o> 2o> 1o> methyl (least stable)

Reaction of Alcohols with Hydrogen Halides

Reaction of Alcohols with other Halogenating agents(SOCl2,PX3)



Dr. Kakul Husain FirozPage 1