Compilation of my Chemistry revision
This is for the 2021 Chemistry AS level OCR course. The chapters follow the same chapters in the OCR Oxford textbook A, up to about half-way, as I only went up to AS-level
First published 4th December 2021
Alcohols, eh, we all love a good old pint of the booze, right? I personally love going down to the pub every day after school, to get myself hammered so far into the ground I barf out my brains. Jk lol, I've only drunk alcohol fumes from nearby adult-drinks, I'm not a naughty criminal like many other youngsters. But this topic isn't really about the different kinds of spirits, lagers and cock-tails, as that would be quite a disadvantage to people with non-poisoned livers like myself. This topic is about alcohols in the Chemistry sense, which is probably similar to alcohols in the Tesco Wine Aisle sense. I've never done it, but I'd assume that whenever you order a drink at a counter you specify how many OH groups the alcohol has, and what kind of oxidation reaction it goes through. If you don't know what that means, have no fear, as you will learn all that below. Before long you'll be able to order any drink you want, whether it is 2-methyl hexan-2,3-diol, or simply ethanol.
So the first important part of alcohols is how they are identified, which is with an -ol suffix (or hydroxy- prefix) on a chemical name. If you have 2 alcohols attached to the hydrocarbon chain then it is called diol, and the numbering system matches with how it usually works in organic Chemistry (e.g. pentan-2,3-diol). The functional group of an alcohol is an OH⁻ ion, which attaches to a hydrocarbon chain. They also have relatively high melting and boiling points, because they have hydrogen bonding. They also have permanent dipole-dipole and London forces, but of course Hydrogen is the strongest. This hydrogen bond happens because the O atom (from OH) has 2 lone pairs and is attached to a H atom (hydrogen bonding needs an electronegative atom which is bonded to H, and has a lone pair). Also alcohols are polar molecules. On it's own an alkane or alkene isn't polar, as all the atoms have similar electronegativities, and it is symmetrical. If an OH group is added then because of the larger difference in electronegativities between O and H, then the now alcohol is now electronegative. Also with alcohols being polar comes with those properties, like being more soluble in polar solutions (like water).
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Before we get onto the reactions (I know you're trembling in anticipation), we need to know to classify the alcohols, which shows the number of carbon atoms bonded to the carbon bonded with the OH group. That made it sound complicated, but it isn't really. We classify them as primary, secondary and tertiary, like with alkenes. Primary alcohols have 1 or 0 carbons bonded to the carbon with the OH group. This means an alcohol group bonded to a carbon at the end of a chain or methane it a primary alcohol. For example, the alcohol in butan-1-ol, or any in methantetraol. Secondly, a secondary alcohol has an OH group bonded to a carbon bonded to 2 carbons. This would be in the middle of a carbon chain (without a methyl group on the top). E.g. propan-2-ol. Lastly, a tertiary alcohol has 3 carbons bonded to the carbon bonded to the OH. This would be in the middle of a chain, with a methyl group on the top, e.g. 2-methyl-butan-2-ol.
