Question

Are alkyl cyanide and alkyl isocyanide isomeric with respect to each other ?Mention their structural difference.
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Answer 1

Cyanides are derivatives of hydrogen cyanide (HCN). The hydrogen atom of HCN is replaced by an alkyl or 
aryl group to give cyanides.
General formula of cyanides is RCN where R is an alkyl or aryl group.

The alkyl group may also be attached to the - CN group through the nitrogen atom, i.e. R – N C. 


Cyanides and isocyanides are thus isomeric.



Nomenclature

Cyanides
In the common system, cyanides are named as alkyl cyanides. The parent alkane is chosen and the 
ending 'e’ replaced by ’yl’ followed by suffix ’cyanide’.
Parent alkane: methane
Common name: Methyl cyanide

They may also be named on the basis of the acid they produce on hydrolysis. The ending ’ic acid’ 
of the acid is replaced by ’onitrile’.

e.g. CH3CN 

Acid produced on hydrolysis:   CH3COOH Acetic acid

Common name: Acetonitrile

According to the IUPAC system, the following rules are followed:

The longest carbon chain carrying the — CN group is considered as the parent alkane.Nitriles in which the -COOH group of an acid (named by a-carboxylic acid suffix) has been replaced by the group, are named by replacing that suffix by the word carbonitrile.
e.g. 

The suffix ’nitrile’ is introduced after the name of the parent alkane (alkane nitrile).
Any substituent is indicated by the appropriate number (with - CN group at position 1).

Structural formulaCommon nameIUPAC nameCH3CNMethyl cyanide or AcetonitrileEthane nitrileCH3CH2CNEthylcyanide or PropiononitrilePropane nitrileCH3CH2CH2CNPropylcyanide ButyronitreButane nitrileCH3 = CH CNVinyl cyanide or AcrylonitrileProp-2-enenitrile    CH3    |CH3     —     CH CN  Iso-propyl cyanide or Isobutyronitrile2-MethylpropanenitrilePhenyl cyanide or BenzonitrileBenzenenitrile   

Isocyanides 
Unlike cyanides, isocyanides have only common names.
In the common system, Isocyanides are named as a Alkyl isocyanides. The parent alkane is chosen 
and the ending ’e’ replaced by ’yl’ followed by suffix ’isocyanide’.
e.g. CH3NC
Parent alkane: Methane
Common name : Methyl isocyanide

They may also be named as alkyl carbylamines.
e.g. CH3NC 
Parent alkane: Methane
Common name: Methyl carbylamine.

Structural FormulaCommon NameCH3 NCMethyl isocyanide or Methyl carbylamineCH3 CH2 NCEthyl isocyanide or Ethyl carbylamineCH3 CH2 CH2 NCPropyl isocyanide or Propyl carbylamineC6H5 NCPhenyl isocyanide or Phenyl carbylamine

Generally, isocyanides are known by common names.

Preparation

From acid amides: