What is meant by the following terms ? Give an example of the reaction in each case.
(i) Cyanohydrin                     (ii) Acetal                       (iii) Semicarbazone
(iv) Aldol                               (v) Hemiacetal               (vi) Oxime
(vii) Ketal                              (vii) Imine                      (ix) 2,4-DNP-derivative
(x) Schiffs base

(i) Cyanohydrin :
-OH group and cyano group are present on same carbon atom. Addition of HCN to carbonyl group in weakly acidic medium forms cyanohydrin.
$C{H}_{3}CHO+HCN\stackrel{pH9-10}{\to }C{H}_{3}CH(OH)CN$

(ii) Acetal :
Terminal C atom has two alkoxy groups. Two equivalents of monohydric alcohol add to 1 equivalent of aldehyde in presence of dry HCl gas.
$C{H}_{3}CHO+2C{H}_{3}OH\stackrel{DryHCl}{\to }C{H}_{3}CH(OC{H}_3{)}_2+H_{2}O$

(iii) Semicarbazone :
Derivative of aldehyde or ketone obtained on treatment with semicarbazide in weakly acidic medium.
$H_{3}CCHO+H_{2}NNHCON{H}_2\underset{-H_{2}O}{\overset{pH3.5}{\to }}C{H}_{3}CH=NNHCON{H}_2$

(iv) Aldol    :                           
Beta hydroxy aldehyde or ketone obtained by condensation of 2 molecules of aldehydes or ketones containing alpha hydrogen atoms in presence of dilute aqueous base.
$2C{H}_{3}CHO\stackrel{O{H}^{-}}{\to }C{H}_{3}CHOHC{H}_{2}CHO$

(v) Hemiacetal   :            
Gem alkoxy alcohols obtained by addition of one molecule of monohydric alcohol to aldehyde in presence of dry HCl gas.
$C{H}_{3}CHO+C{H}_{3}OH\rightleftharpoons C{H}_{3}CH(OH)OC{H}_3$

(vi) Oxime :
Aldehydes or ketones react with hydroxyl amine in weakly acidic medium
$C{H}_{3}CHO+H_{2}NOH\to C{H}_{3}CH+NOH$

(vii) Ketal  :                            
Gem dilkoxy alkanes obtained by the reaction of ketone with ethylene glycol in presence of dry HCl. Two alkoxy groups are present on same C atom.
$C{H}_{3}COC{H}_3+HOC{H}_{2}C{H}_{2}OH\to (C{H}_3{)}_{2}C(O_C{H}_2-{)}_2$

(vii) Imine :                     
They contain -CH=N- group obtained by the reaction between aldehydes and ketones with ammonia derivatives such as hydrazine, hydroxylamine, phenyl hydrazine, semicarbazide etc.
$C{H}_{3}COC{H}_3+PhNH-N{H}_2\to (C{H}_3{)}_{2}C=NNHPh$

(ix) 2,4-DNP-derivative :
Derivatives obtained by the reaction of aldehydes and ketones with 2,4-DNP (2,4-dinitrophenylhydrazone) in weakly acidic medium.
$C{H}_{3}COC{H}_3+H_{2}NNH-C_6{H}_4(N{O}_2{)}_2\underset{-H_{2}O}{\overset{pH=3.5}{\to }}(C{H}_3{)}_{2}C+NNH-C_6{H}_4(N{O}_2{)}_2$

(x) Schiffs base :
Azomethines obtained by the reaction of aldehydes and ketones with primary amines (aliphatic or aromatic).
$PhCHO+PHN{H}_2\underset{\Delta }{\overset{H^{+}}{\to }}PhCH=NHPh+H_{2}O$