A Level Chemistry OCR Practice Exam

What is an alkyl group?

1. An alkane with an oxygen atom removed

2. An alkane with a hydrogen atom removed

3. An alkane with a carbon atom replaced

4. An alkane with two functional groups

The correct answer is: An alkane with a hydrogen atom removed

An alkyl group is defined as an alkane molecule that has had one hydrogen atom removed, resulting in a substituent that can attach to a larger structure in an organic compound. This removal creates a site for bonding, allowing the alkyl group to function as a part of a more complex molecule. For example, if we take ethane (C2H6) and remove one hydrogen, we form the ethyl group (C2H5−), which can bind to other atoms or groups. The other options do not accurately describe the nature of an alkyl group. Removing an oxygen atom from an alkane does not align with the definition since alkyl groups are hydrocarbon chains. Replacing a carbon atom could result in varied structures, but it does not yield a traditional alkyl group. Lastly, having two functional groups does not specifically characterize an alkyl group since an alkyl group itself is simply a hydrocarbon component, regardless of the presence of other functional groups in the larger molecule.