CambridgeInternationalASandALevelChemistry OriginalmaterialCambridgeUniversityPress2011 1

Worksheet14.1

Alkanesfreeradicalsubstitution

1 Methaneandchlorinereacttogethertogivechloromethaneandhydrogenchloride.a Writeabalancedsymbolequationforthisreaction. [1]b Explainthemechanismforthisreactionusingatleastfoursteps.Youshouldinclude:

aninitiationstep [1] twopropagationsteps [2] aterminationstep. [1]

c Whataretheessentialconditionsfortheinitiationstep? [1]d Drawamoleculeofchloromethane.Labelthebondangles. [2]

2 Ethaneandbrominereacttogethertogivebromoethaneandhydrogenbromide.a Writeabalancedsymbolequationforthisreaction. [1]b Explainthemechanismforthisreactionusingatleastfoursteps.Youshouldinclude:

aninitiationstep [1] twopropagationsteps [2] aterminationstep. [1]

c Whatisneededforthereactiontotakeplace? [1]d Drawthefullstructuralformulaeoftwootherorganicproductsthatmightforminthis

reaction.Explainhoweachcouldbeproduced. [4]

3 Useoneofthereactionsaboveasasourceofexamplestoexplainwhatismeantbythefollowingterms:a radical [2]b substitution [2]c homolyticfission. [2]

4 Explainwhatismeantbyeachofthefollowingterms.Yourexplanationsshouldbeintermsofthenumberoffreeradicalsinvolved.a initiationstep [1]b propagationstep [1]c terminationstep [1]

5 a Completethefollowingequations.i C3H7+Cl2 ? [1]ii C3H7+C3H7 ? [1]iii C3H7+Br2 ? [1]iv Br2 ? [1]v C2H5Cl+Cl HCl+? [1]

b Bromoethanecanbepreparedfromethanebythesubstitutionofhydrogenbybromine.Whatarethe twomainproblemswithusingthismethod? [2]