COAS Chemistry2 Teacher ResourcesOriginal material © Cambridge University Press 2005, 2007, 2009 1
3 Worksheet 1
Aldehydes and ketones: nucleophilic addition
1Propanone and sodium borohydride (NaBH4) react together in the presence of water to give propan-2-ol. The sodium borohydride is a source of hydride ions (H–).
aWrite a balanced chemical equation for this reaction.[1]
bExplain the mechanism for this reaction using curly arrows. You should include:
•the dipole on the propanone molecule at the start
•the attack on the propanone molecule by an electron pair (curly arrow) from the H–ion
•the negatively charged intermediate with the negative charge on the oxygen atom
•the movement of two electrons from the oxygen (curly arrow) to make a bond to a hydrogen ion from water. [4]
2Propanal and sodium borohydride (NaBH4) react together in the presence of water to give
propan-1-ol. The sodium borohydride is a source of hydride ions (H–).
aWrite a balanced chemical equation for this reaction.[1]
bExplain the mechanism for this reaction using curly arrows. You should include:
•the dipole on the propanal molecule at the start
•the attack on the propanal molecule by an electron pair (curly arrow) from the H–ion
•the negatively charged intermediate with the negative charge on the oxygen atom
•the movement of two electrons from the oxygen (curly arrow) to make a bond to
a hydrogen ion from water.[4]
3Use one of the reactions in questions 1 and 2 as a source of examples to explain what is
meant by:
aa nucleophile
baddition
cheterolytic fission [6]
4aDraw skeletal formulae of:
ipentan-2-one
iipropanal
iii3,3-dimethylbutan2-one
iv3-methylbutan-2-one
vpropanone
vihexanal[6]
bSort the carbonyl compounds in part a into three isomeric pairs.[3]
cGive the structural formula of the product when each of the carbonyl compounds in part a
is reduced by aqueous hydride ions (H–).[6]
Total: Score: %
COAS Chemistry2 Teacher ResourcesOriginal material © Cambridge University Press 2005, 2007, 2009 1