Author: J R Reid Organics – Naming the Molecules Types Chain lengths Add–ons Specific naming

Naming - Introduction In organic chemistry the names of each molecules has three main parts: The type of chemical e.g. Alkane The length of its longest carbon chain The add–ons to the main chain of carbons When we put them together into the name we use the order: Add–on : Length of chain : Type of organic To make life interesting, we give codes to help us so that we don’t have to write: One chlorine is attached to the second carbon in a chain five carbons long in an alkane

Naming - Types As we have seen already there are a few different types of organic chemicals. Each one is given a specific code name that gets tacked on as a suffix (end of a word) TypeSuffixExample Alkane-anepropane Alkene-enepropene Alkyne-ynepropyne Alkanol-olpropanol Carboxylic acid -oic acid propanoic acid Ester-oatemethyl propanoate

Naming – Chain Length The organic molecules can come in a number of lengths e.g. 1 carbon, 2 carbons… The number of carbons in the main chain of the molecule forms a prefix (beginning of a word) for the name NumberPrefixExample 1Meth- Meth ane 2Eth- Eth ene 3Prop- Prop yne 4But- But anol 5Pent- Pent ane 6Hex- Hex ene 7Hept- Hept yne 8Oct- Oct anol 9Non- Non ane 10Dec- Dec ene

Naming – Add-ons I The main chain can have stuff added to it. These might be extra carbon branches or halogens. It is important for us to be able to know exactly what and where they are. This forms the very first part of the name (before the prefix). Here is how we do it: Count the number of carbons in from the closest side (along the main chain). This forms the number that goes at the front of the name Next write the code for the add-on Add-onCode 1 carbonmethyl 2 carbon chain ethyl 3 carbon chain propyl Chlorinechloro Brominebromo e.g. 2 methyl pentane

Naming – Add-ons II Some times they add more than on add-on. This means that the name needs to show us how many there are and where we can find them. To do this we need to: Add all the numbers showing where each add-on is found Sometimes the add-on code needs a prefix telling us how many there are Number of the same add-ons Prefix 2di- 3tri- 4tetra- e.g. 2,3 dimethyl butane

Practice

Specific Naming Rules– Alkenes and Alkynes Some types have extra part to their name specifically telling us where certain features can be found: Alkenes – we need to know where the double bond is. In this case we count in from the closest side – if the double bond is on the first bond of a pentene we would call it pent-1-ene Alkynes – the same rule applies e.g. oct-3-yne

Specific Naming Rules – Alkanols (Alcohols) Naming and alcohol is very similar to naming alkenes and alkynes. This is because the location of the –OH group on the chain is very important In this case we number the carbon (from the closest end) and locate which carbon the –OH is on. For example, ‘ propan-1-ol ’ means that the –OH is on the first (number 1) carbon. ‘Propan-2-ol’ has the –OH on the second carbon Why is there no such chemical as ‘ propan-3-ol’ ?

Specific Naming Rules - Esters Esters are made when we react an alcohol with a carboxylic acid. Unfortunately they are difficult to name because they have a break in their carbon chain. We therefore have to add two parts to their name: The part from the alcohol comes first. Its name comes from how many carbons it has e.g. methyl, ethyl, propyl… etc The part from the carboxylic acid comes last. It ends in ‘-oate’ e.g. methanoate, ethanoate, propanoate… etc. You can always tell which part came from an acid, because acids have more oxygen atoms Acid half = butanoate Alcohol half = ethyl Ethyl butanoate

Practice II