Esters – Structures and Names
- Identify the general structure for an ester.
- Use common names to name esters.
- Name esters according to the IUPAC system.
Esters have the general formula RCOOR′, where R may be a hydrogen atom, an alkyl group, or an aryl group, and R′ may be an alkyl group or an aryl group but not a hydrogen atom. (If it were hydrogen atom, the compound would be a carboxylic acid.) Figure 220.127.116.11.1 shows models for two common esters.
Figure 18.104.22.168.1: The Structure of Esters. Esters feature a carbon-to-oxygen double bond that is also singly bonded to a second oxygen atom, which is then joined to an alkyl or an aryl group. The esters shown here are ethyl acetate (a) and methyl butyrate (b).
Esters occur widely in nature. Unlike carboxylic acids, esters generally have pleasant odors and are often responsible for the characteristic fragrances of fruits and flowers. Once a flower or fruit has been chemically analyzed, flavor chemists can attempt to duplicate the natural odor or taste. Both natural and synthetic esters are used in perfumes and as flavoring agents.
Fats and vegetable oils are esters of long-chain fatty acids and glycerol. Esters of phosphoric acid are of the utmost importance to life.
Names of Esters
Although esters are covalent compounds and salts are ionic, esters are named in a manner similar to that used for naming salts. The group name of the alkyl or aryl portion is given first and is followed by the name of the acid portion. In both common and International Union of Pure and Applied Chemistry (IUPAC) nomenclature, the –ic ending of the parent acid is replaced by the suffix –ate (Table 22.214.171.124.1).
Give the common and IUPAC names for each compound.
- The part of the molecule derived from the carboxylic acid (in red) has three carbon atoms. It is called propionate (common) or propanoate (IUPAC). The ester is therefore butyl propionate or butyl propanoate.
- An alkyl group (in green) is attached directly to the oxygen atom by its middle carbon atom; it is an isopropyl group. The part derived from the acid (that is, the benzene ring and the carbonyl group, in red) is benzoate. The ester is therefore isopropyl benzoate (both the common name and the IUPAC name).
Draw the structure for ethyl pentanoate.
Start with the portion from the acid. Draw the pentanoate (five carbon atoms) group first; keeping in mind that the last carbon atom is a part of the carboxyl group.
Draw the structure for phenyl pentanoate.
Nomenclature of Esters
Esters are known for their distinctive odors and are commonly used for food aroma and fragrances. The general formula of an ester is RCOOR’.
Esters are formed through reactions between an acid and an alcohol with the elimination of water. An example of this is the reaction of acetic acid with an alcohol, which yields an acetic ester and water.
The part enclosed by the red circle represents the ethyl group from the alcohol and the part enclosed by the green rectangle represents the acetate group from the acid.
Esters can be named using a few steps
Esters are named as if the alkyl chain from the alcohol is a substituent. No number is assigned to this alkyl chain. This is followed by the name of the parent chain from the carboxylic acid part of the ester with an –e remove and replaced with the ending –oate.
Esters are formed through reactions between an acid and an alcohol with the elimination of water. An example
1. First, identify the oxygen that is part of the continuous chain and bonded to carbon on both sides. (On one side of this oxygen there will be a carbonyl present but on the other side there won’t be.)
2. Second, begin numbering the carbon chains on either side of the oxygen identified in step 1.
3. Next, use this format: [alkyl on side further from the carbonyl] (space) [alkane on the side with the carbonyl] – (In this case: [methyl] [methane])
4. Finally, change the ending of the alkane on the same side as the carbonyl from -e to -oate. (In this case: methyl methanoate)
When an ester group is attached to a ring, the ester is named as a substituent on the ring.
Benzenecarboxylic acid (Benzoic acid)
Other substituents that exist on either side of the ester are named in the same way as they are on regular alkane chains. The only thing you must make sure of is placing the substituent name on the part of the name that corresponds to the side of the ester that it is on.
Name the following:
Concept Review Exercises
- From what carboxylic acid and what alcohol can isopropyl hexanoate be made?
- From what carboxylic acid and what alcohol can cyclobutyl butyrate be made?
- hexanoic acid and isopropyl alcohol
- butyric acid and cyclobutyl alcohol
- An ester has an OR group attached to the carbon atom of a carbonyl group.
- Draw the structure for each compound.
- methyl acetate
- ethyl pentanoate
- phenyl acetate
- isopropyl propionate
- Draw the structure for each compound.
- ethyl hexanoate
- ethyl benzoate
- phenyl benzoate
- ethyl 3-methylhexanoate
- Name each compound with both the common name and the IUPAC name.
3. a methyl formate; methyl methanoate
b. ethyl propionate; ethyl propanoate
What is Ester?
The first thing that we need to do is understand what is Ester? Well, to answer that question, according to the common definition, It is basically a chemical compound that is derived from an organic or inorganic acid in which at least hydroxyl (-OH) group is replaced by an alkyl (-O-) group. To put it in simple terms, esters are the group of chemical compounds which are formed by bonding of an alcohol group with a group of organic acids, by losing water molecules.
Esters are also usually derived from carboxylic acids. It may also be obtained by reaction of acid anhydride or acid halides with alcohols or by the reaction of salts of carboxylic acids with alkyl halides.
What is Esterification?
This is another term that we need to learn and understand this topic. Esterification is a process or a general name for a chemical reaction, in which two reactants (alcohol and an acid) form an ester as the reaction product. The formula for carboxylic acid esters is RCOOR’ (where R and R’ are any organic combining groups) that are prepared again by the reaction of alcohols and carboxylic acids in the presence of hydrochloric acid or sulphuric acid is done by this process. Through this process, we basically learn about the formation of esters.
To give you an example of an ester, we can talk about ethyl ethanoate. Here, the hydrogen in the -COOH group is replaced by an ethyl group. You can find the ethyl ethanoate formula below:
In this case, the ester is usually named in the opposite way around from the way the formula is written. In this case, “ethanoate” part comes from ethanoic acid and the “ethyl” part comes from the ethyl group on the end.
Uses of Esters
It is a sweet-smelling substance. Some of them are used as food flavourings and other esters are used as fragrances or perfumes. Apart from that, they can be turned into polymers dubbed as polyesters which can be used to make cans or plastic bottles.
Here are some other users of esters:
- Esters that have fragrant odours are used as a constituent of perfumes, essential oils, food flavourings, cosmetics, etc
- It is used as an organic solvent
- Natural esters are found in pheromones.
- Naturally occurring fats and oils are fatty acid esters of glycerol.
- Nitrate esters, such as nitroglycerin, are used as explosive materials.
- Polyesters can be further converted into fibres to make clothing.
- It is used to make surfactants E.g. soap, detergents.
Frequently Asked Questions – FAQs
What is ester used for?
In synthetic flavours, perfumes, and cosmetics, these and other toxic esters with distinctive odours are used. Some volatile esters are used as solvents for coatings, paints and varnishes; significant amounts of ethyl acetate and butyl acetate are manufactured commercially for this purpose.
What is an ester in chemistry?
A compound or functional group derived from alcohol condensation and an acid with simultaneous water loss. Carboxylic ester (also referred to as carboxylate ester; also simply called an ester), derived from carboxylic acid, is the most common form of ester.
Why do esters smell?
Esters smell partially because of the feeble intermolecular forces they show. This encourages ester molecules to penetrate and hit the nose in the gas phase. To share in hydrogen bonding, there are not highly positively polarised hydrogens in esters. Remember ethyl butyrate, for instance, which smells like pineapple.
How ester is formed?
The condensation reaction between an alcohol and a carboxylic acid produces esters. This is referred to as esterification. Two molecules combine and create a larger molecule in a condensation reaction thus removing a tiny molecule. This small molecule, during esterification, is water.
What is the functional group of ether?
Ethers are a class of organic compounds containing an ether group, an atom of oxygen bound to two classes of alkyl or aryl. They have the general R-O-R’ formula, where the alkyl or aryl groups describe R and R’.