In organic chemistry principle provides for the two properties, namely 1.1-substitution and 1,2 substitution ,What is the difference between the two ?

1,1 substitution &1,2 substitution takes place only in compounds with more than two carbon(here ''C" an example) atoms .

1,1 substitutions means substituting any atom in the first carbon atom in the compound(numbering of carbon is based on IUPAC rule)

2,2 substitution means substituting any atom adjacent to the first carbon atom

EXAMPLE1,1 SUBSTITUTION

CH3-CH2-CH2-Br reacts with NaCn gives CH3-CH2-CH2-CN + NaBr (fast reaction)

Here, Br atom is in the first C atom and that C atom is numbered as FIRST carbon C) atom.The adjacent to the first C atom is the second and so on....

Here the reagent NaCn ,Nais +ve and CN is in the -ve state moreover the CN-is highly electronegative than Br atom

substitution is based on number of factors

1.the electronegativity of the substituting agent

2.the stereo chemistry of the main group

3.steric hinderence of any group associated with the main group

4.electrophile or nucleophile present in the main chain.

5.presents of leaving group 

there are two types of substitution 

1.ELECTROPHILIC SUBSTITUTION

2.NUCLEOPHILIC SUBSTITUTION

ie, Aromatic or Aliphatic substitution reactions

these2 subsitutions give us isomers, molecules with identical type and number of atoms, but different arrangmennt.

1,1 is when the new atoms are added to the same atom 

1,2 is when the new atoms are added to adjacent atoms

the atom is usually a carbon

this is related mostly to the electronegativity of the reacting molecules, and their arrangment hence the steric hindrance.

other types include1,3 -1,4 -2,3 -2,4.. and many more

counting usually starts at the double bond

the1,1 subtitution indicate that the two element are substituted in carbon number one 

the1,2 subtitution indicate that the substitution is hapened one element in carbone number one the other in carbone number two

such us the notification of the number of carbone in an organic product is with international convensatin