EasyChemistryHigh School (11–12)Organic Chemistry: Some Basic Principles and Techniques › Electronic Effects and Reaction IntermediatesConceptualA-LevelIB
Three bonds break as shown below. For each, say whether the fission is homolytic or heterolytic…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Three bonds break as shown below. For each, say whether the fission is homolytic or heterolytic, name the two pieces, and say which kind of curved arrow you would draw.
- The Br-Br bond of is split by light.
- The C-Cl bond of breaks in a polar solvent. Chlorine is the more electronegative atom.
- The O-O bond of a peroxide, , breaks on heating.
Need a reminder? The key ideaShow
A covalent bond breaks by homolytic or by heterolytic fission. In homolytic fission each atom keeps one electron. This gives free radicals and is drawn with half-headed arrows. In heterolytic fission one atom takes both electrons. This gives a cation and an anion and is drawn with a full-headed arrow. A carbocation is flat and has six electrons. A carbanion is pyramidal with a lone pair. Alkyl groups and hyperconjugation make a carbocation or radical more stable: tertiary, secondary, primary, methyl. The order for a carbanion is the reverse.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
(a) Homolytic. The pieces are two bromine atoms, , which are free radicals. Draw two half-headed arrows, one for each electron.
(b) Heterolytic. Chlorine takes both electrons. The pieces are , a carbocation, and , an anion. Draw one full-headed arrow from the bond to chlorine.
(c) Homolytic. The pieces are two radicals. Draw two half-headed arrows.
Answer: (a) and (c) give free radicals. (b) gives a cation and an anion.
Discussion (0)
Log in to join the discussion.
Loading…