In today’s lesson, we are going to discuss nomenclature and properties of the following organic functional groups:
1. Anhydrides
2. Acyl Halides (eg. Acid Chlorides)
3. Nitriles
Anhydrides
Note: “Anhydrides” and “Acid Anhydrides” are different names for the same family. Anhydrides are compounds that have 2 carbonyl groups separated by an Oxygen in the shape. Anhydride means “to lose water,” because a water molecule is lost in the formation reaction of an anhydride. Take a look at this example below, with the anhydride group highlighted.
To name this, we separate the chain by the Oyxgen. Name these in alphabetical order. We use the first prefix + “anoic” + second prefix + “anoic” + “anhydride.” See how I have numbered the shape below, counting outwards from the carbonyl groups.
We have an “eth” on the right (2 carbon chain) and a “prop” on the left (3 carbon chain). Connecting “anoic” to these, putting them in alphabetical order (eth before prop), and putting “anhydride” at the end, we get ethanoic propanoic anhydride.
Properties of Anhydrides
(a) Polarity: The carbonyl groups are polar but the rest of the shape is not.
(b) Boiling Point: Not as high as a carboxylic acid because there are no hydrogen bonds.
Acyl Halides
An acyl halide is also called an acid halide. This is a carbonyl group connected to a halogen. To name these, we number the carbon chain starting from the carbonyl carbon as #1.
This is named in two parts: Prefix of the main chain + “anoyl” as the first part. For the second part, name the halogen with an “ide” ending (Eg. chloride, fluoride, bromide, iodide, etc). Take a look at the example below where the acyl halide part of the chain is highlighted.
This is a 3 carbon chain and the prefix is prop. We add “anoyl.” Then leave a space and put “bromide” because we have a bromine but change the ending to -ide. This gives propanoyl bromide. If there are any substituents, put it before the “propanoyl” part.
You may have heard of a more common functional family called an Acid Chloride. This is a type of acyl halide as well.
Properties of Acyl Halides
(a) Color: Colorless
(b) Solubility: Insoluble in water because they often react violently instead, to make carboxylic acids and hydrogen halides
(c) Polarity: Same as anhydrides
(d) Boiling Point: Higher than an alkane of similar size, but lower than a compound that has Hydrogen Bonding, such as an alcohol or carboxylic acid
Nitriles
A cyano functional group is a Carbon triple bonded to a Nitrogen, and any compound that contains this group is called a Nitrile. Take a look at this example below, where the cyano group is highlighted.
We name these as alkane + “nitrile.” This is a 4 carbon chain, so it is a butane when named as an alkane (Include the carbon in the cyano group). We end the name with “nitrile” so it is a butanenitrile, with no spaces.
We can also name it as substituent + “cyanide.” There are 3 carbons coming out of the cyano group (not including the CN carbon itself), and as a substituent this is propyl. Putting it together with “cyanide” and leaving a space in between, we get propyl cyanide.
Properties of Nitriles
(a) Color: Colorless
(b) Polarity: Very polar (but they don’t have hydrogen bonds within them – they can hydrogen bond with other molecules though). They are soluble in water, but solubility decreases with a longer hydrocarbon (non-polar) chain
(c) Phase: Lower molar mass nitriles are in the liquid phase at room temperature.