Chemguide: Support for CIE A level Chemistry

Learning outcome 15: Halogen compounds

15.1: Halogenoalkanes

Statement 15.1.1

This statement is about how halogenoalkanes might be produced chemically.

Halogenoalkanes are compounds in which one or more of the hydrogens in an alkane have been replaced by a halogen atom. A commonly discussed molecule is bromoethane, CH3CH2Br, where one of the hydrogen atoms in ethane has been replaced by a bromine atom.

Statement 15.1.1(a)

You should find and read the statement in your copy of the syllabus.

This deals with the reaction of alkanes with chlorine or bromine in the presence of UV light.

It is true that halogenoalkanes are what are formed when you react an alkane with chlorine or bromine under these conditions, but you would never choose to do this as a way of preparing a sample of the halogenoalkane. You end up with a difficult-to-separate mixture.

This is dealt with on the page The halogenation of alkanes.

Statement 15.1.1(b)

Again, find and read the statement in your syllabus.

If you are working through the syllabus in order, you will already have met these reactions as a part of alkene chemistry.

The reactions with halogens are covered on the page The halogenation of alkenes.

The reactions with hydrogen halides are covered on the page Alkenes and hydrogen halides.

Statement 15.1.1(c)

This statement is a complicated part of the chemistry of alcohols. I suggest that you don't even bother to look at it now, but leave it until it appears as a part of alcohol chemistry in statement 16.1.2(b). I will refer you back to the current Section 15 statement when it becomes relevant.

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© Jim Clark 2020