Nomenclature of Esters

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Nomenclature of Esters Table of Contents 1. Introduction 2. Esters can be named using a few steps 1. Benzenecarboxylic acid (Benzoic acid) 2. 1-chloromethyl ethanoate 3. methyl 1-chloroethanoate 4. methyl propanoate 3. octyl ethanoate 4. References 5. Outside Links 6. Problems 7. Contributors Esters are known for their distinctive odors and are commonly used for food aroma and fragrances. The general formula of an ester is RCOOR'. Introduction 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.

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Nomenclature of Esters

Transcript of Nomenclature of Esters

Page 1: Nomenclature of Esters

Nomenclature of EstersTable of Contents

1. Introduction   2. Esters can be named using a few steps

1. Benzenecarboxylic acid (Benzoic acid) 2. 1-chloromethyl ethanoate 3. methyl 1-chloroethanoate 4. methyl propanoate

3. octyl ethanoate     4. References 5. Outside Links 6. Problems 7. Contributors

Esters are known for their distinctive odors and are commonly used for food aroma and fragrances. The general formula of an ester is RCOOR'.

Introduction 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.

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Esters can be named using a few stepsEsters 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.

Example

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)

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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.

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1-chloromethyl ethanoate

methyl 1-chloroethanoate 

CH3COOCH2CH3

methyl propanoate

CH3COOCH2CH2CH2CH2CH2CH2CH2CH3                                    

octyl ethanoate    

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The IUPAC system of nomenclature assigns a characteristic suffix to these classes. The –e ending is removed from the name of the parent chain and is replaced -anoic acid. Since a carboxylic acid group must always lie at the end of a carbon chain, it is always is given the #1 location position in numbering and it is not necessary to include it in the name. 

Many carboxylic acids are called by the common names. These names were chosen by chemists to usually describe a source of where the compound is found. In common names of aldehydes, carbon atoms near the carboxyl group are often designated by Greek letters. The atom adjacent to the carbonyl function is alpha, the next removed is beta and so on.

 

Formula Common Name Source IUPAC Name Melting Point Boiling Point

HCO2H formic acid ants (L. formica) methanoic acid 8.4 ºC 101 ºC

CH3CO2H acetic acid vinegar (L. acetum) ethanoic acid 16.6 ºC 118 ºC

CH3CH2CO2H propionic acid milk (Gk. protus prion) propanoic acid -20.8 ºC 141 ºC

CH3(CH2)2CO2H butyric acid butter (L. butyrum) butanoic acid -5.5 ºC 164 ºC

CH3(CH2)3CO2H valeric acid valerian root pentanoic acid -34.5 ºC 186 ºC

CH3(CH2)4CO2H caproic acid goats (L. caper) hexanoic acid -4.0 ºC 205 ºC

CH3(CH2)5CO2H enanthic acid vines (Gk. oenanthe) heptanoic acid -7.5 ºC 223 ºC

CH3(CH2)6CO2H caprylic acid goats (L. caper) octanoic acid 16.3 ºC 239 ºC

CH3(CH2)7CO2H pelargonic acid pelargonium (an herb) nonanoic acid 12.0 ºC 253 ºC

CH3(CH2)8CO2H capric acid goats (L. caper) decanoic acid 31.0 ºC 219 ºC

Example (Common Names Are in Red)

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Naming carboxyl groups added to a ringWhen a carboxyl group is added to a ring the suffix -carboxylic acid is added to the name of the cyclic compound. The ring carbon attached to the carboxyl group is given the #1 location number.

 

Naming carboxylatesSalts of carboxylic acids are named by writing the name of the cation followed by the name of the acid with the –ic acid ending replaced by an –ate ending. This is true for both the IUPAC and Common nomenclature systems.

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Naming carboxylic acids which contain other functional groupsCarboxylic acids are given the highest nomenclature priority by the IUPAC system. This means that the carboxyl group is given the lowest possible location number and the appropriate nomenclature suffix is included. In the case of molecules containing carboxylic acid and alcohol functional groups the OH is named as a hydroxyl substituent. However, the l in hydroxyl is generally removed. 

In the case of molecules containing a carboxylic acid and aldehydes and/or ketones functional groups the carbonyl is named as a "Oxo" substituent. 

In the case of molecules containing a carboxylic acid an amine functional group the amine is named as an "amino" substituent. 

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When carboxylic acids are included with an alkene the following order is followed:

(Location number of the alkene)-(Prefix name for the longest carbon chain minus the -ane ending)-(an –enoic acid ending to indicate the presence of an alkene and carboxylic acid)

Remember that the carboxylic acid has priority so it should get the lowest possible location number. Also, remember that cis/tran or E/Z nomenclature for the alkene needs to be included if necessary. 

Naming dicarboxylic acidsFor dicarboxylic acids the location numbers for both carboxyl groups are omitted because both functional groups are expected to occupy the ends of the parent chain. The ending –dioic acid is added to the end of the parent chain. 

 

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Section 12.3: Thioesters1. 12.3A: Introduction to thioesters and Coenzyme A 2. 12.3B: Activation of fatty acids by coenzyme A: a thioesterification reaction 3. 12.3C: Transfer of fatty acyl groups to glycerol: a thioester to ester substitution 4. 12.3D: Transthioesterification reactions 5. 12.3E: Hydrolysis of thioesters 6. Contributors

12.3A: Introduction to thioesters and Coenzyme AAcyl phosphates and acyl adenosine phosphates are not the only activated forms of carboxylate groups in biochemical reactions.  Slightly lower on the reactivity scale are thioesters. In the metabolism of lipids (fats and oils), thioesters are the principal form of activated carboxylate groups.  They are employed as acyl carriers, assisting with the transfer of acyl groups such as fatty acids from one acyl X substrate to another. 

The ‘acyl X group’ in a thioester is a thiol. The most important thiol compound used to make thioesters is called coenzyme A, which has the following structure:

Coenzyme A is often abbreviated HSCoA, in order to emphasize that it is the thiol sulfur that provides the critical thioester linkage to acyl groups.  When fuel (carbohydrate and fat) is broken down in your body, it is eventually converted to a simple two-carbon unit called acetyl CoA, which is essentially a thioester derivative of acetic acid:

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12.3B: Activation of fatty acids by coenzyme A: a thioesterification reactionIn the biologically active form of fatty acids, the carboxylate groups have been converted to thioesters using coenzyme A.  For example, the activated form of the C16 fatty acid palmitate is:

Let’s take a look at how this activation takes place, in a reaction catalyzed by an enzyme called acyl CoA synthetase. You already know that carboxylates are not themselves good substrates for acyl substitution reactions, and must be activated. Thus, you might predict that the first step of this reaction requires ATP to make a high-energy acyl phosphate intermediate. In fact, the activated carboxylate in this case is an acyl-AMP, formed in the same way as the acyl-AMP intermediate in the asparagine synthetase reaction (section 12.2B).

The activated acyl-AMP intermediate is then attacked by the thiol sulfur of coenzyme A, and the AMP group is expelled to form the fatty acyl CoA. 

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12.3C: Transfer of fatty acyl groups to glycerol: a thioester to ester substitutionThe -SCoA thioester form of the fatty acid is a good substrate for a number of metabolic transformations.  This is the form of fatty acid, for example, that is oxidized and broken down for energy in the mitochondria of your cells.  Fatty acyl CoA also serves as substrate for the construction of triacylglycerol, which is the fat molecule that your body uses to store energy in fat cells.  Recall (section 12.1B) that triacylglycerol is composed of a glycerol ‘backbone’ connected to three fatty acid groups through ester linkages.

The reaction in which a fatty acid acyl group is linked to glycerol represents the conversion of a thioester (fatty acyl CoA) to an ester.  First, however, a transthioesterification reaction occurs.  A transthioesterification is merely the conversion of one thioester to another.  In the case of monoacylglycerolacyltransferase, the fatty acyl group first trades its thioester link to coenzyme A for another thioester link to a cysteine residue in the active site of the enzyme. It is a common

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strategy for enzymes to first form a covalent link to one substrate before catalyzing the principle chemical reaction.

The fatty acyl group is now ready to be transferred to glycerol, trading its thioester linkage to the cysteine for a new ester linkage to one of the alcohol groups on glycerol. The attacking nucelophile in this reaction is of course the alcohol oxygen of monoacylglycerol.

Because esters are more stable than thioesters, this is an energetically downhill reaction.

 

12.3D: Transthioesterification reactionsIn the previous section we saw one example of a transthioesterification.  Another important transthioesterification reaction involves acetyl CoA, the activated form of acetic acid and the basic two-carbon building block for fats and oils.  Before it can be incorporated into a growing fatty acid molecule, acetyl CoA must first be linked to a so-called ‘acyl carrier protein’ (ACP). The acetyl group is linked to the acyl carrier protein via a thiol group on a carrier molecule that is covalently attached to the protein. 

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Notice that the structure of this carrier group (called phosphopantetheine) is identical to the region of coenzyme A  (structure shown earlier in this section) near the thiol group.  Once attached to the ACP, the two-carbon acetyl group condenses with another acyl group (which is also attached to its own ACP), and the fatty acid chain begins to grow.  We will study these important carbon-carbon bond forming reactions in section 13.4.

Finally, a transthioesterification is the final step in one of the most important and well-studied reactions in animal metabolism: the conversion of pyruvate to acetyl CoA by a cluster of enzymes called the pyruvate dehydrogenase complex.

The overall reaction looks simple, but is actually quite complex and involves several intermediate species. The final step in the process is a transthioesterification, involving a dithiol molecule called lipoamide:

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We will look more closely at the complete biochemical transformation catalyzed by the pyruvate dehydrogenase complex in section16.12B.

 

12.3E: Hydrolysis of thioestersThe acyl group of a thioester can be transferred to a water molecule in a hydrolysis reaction, resulting in a carboxylate. An example of thioester hydrolysis is the conversion of (S)-citryl CoA to citrate in the citric acid cycle (also known as the Krebs cycle).

In later sections of this chapter we will see examples of ester and amide hydrolyses.

Basic IUPAC Organic Nomenclature

AmidesNomenclature Formula 3D structureFunctional class name = alkyl alkanamide

Substituent suffix = -amide 

1. Amides are amine derivatives of carboxylic acids.

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2. The root name is based on the longest chain including the carbonyl group of the amide group.

3. Since the amide group is at the end of the chain, the C=O carbon must be C1.

4. The amide suffix is appended after the hydrocarbon suffix minus the "e" : e.g.  -ane + -amide = -anamide etc.

5. If the amide nitrogen is substituted, the these substituents are given N- as the locant.

6. The N- locant is listed first.

Functional group is an amide therefore suffix = -amideHydrocarbon structure is an alkane therefore -an-The longest continuous chain is C4 therefore root = but

butanamideCH3CH2CH2C(=O)NH2

Functional group is an amide therefore suffix = -amideHydrocarbon structure is an alkane therefore -aneThe longest continuous chain is C4 therefore root = butThe nitrogen substituent is C1 i.e. an N-methylgroup

N-methylbutanamideCH3CH2CH2C(=O)N(CH3)H

Functional group is an amide therefore suffix = -amideHydrocarbon structure is an alkane therefore -aneThe longest continuous chain is C2 therefore root = ethThe two nitrogen substituents are C1 i.e. an N-methyl groupThere are two methyl groups, therefore multiplier = di-

N,N-dimethylethanamideCH3C(=O)N(CH3)2

©Dr. Ian Hunt, Department of Chemistry

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Nomenclature of NitrilesName the parent alkane (include the carbon atom of the nitrile as part of the parent) followed with the word -nitrile. The carbon in the nitrile is given the #1 location position.  It is not necessary to include the location number in the name because it is assumed that the functional group will be on the end of the parent chain.

Cycloalkanes are followed by the word -carbonitrile. The substituent name is cyano.

1. 1-butanenitrile or 1-cyanopropane

Try to name the following compounds using these conventions�

  J

  J

Try to draw structures for the following compounds�

1. butanedinitrile J2. 2-methycyclohexanecarbonitrile J

 

Some common names that you should know are...

  acetonitrile

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  benzonitrile

Try to draw a structure for the following compound�

1. 2-methoxybenzonitrile J

1. According to Ms. Duckworth the things you learn in 7th Grade Math are the following except:

2. Ratios

3. Polynomials

4. The area of parallelogram

5. Decimals

6. According to Ms. Duckworth what did she do after teaching?

1. Went to Graduate school to study Psychology

2. Went to the Westpoint Military Academy

3. Went to private companies

4. She never left teaching

What are the characteristics she measured when she gave out the questionnaires to the selected students of the Chicago public high school?

A. Talents of an individual

B. Standardized achievement test score

C. How safe kids felt at school

D. Family income