Carboxyl Group

7 Key excerpts on "Carboxyl Group"

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  eBook - ePub

  Chemistry

  With Inorganic Qualitative Analysis

  • Therald Moeller(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  32

  ORGANIC CHEMISTRY: FUNCTIONAL GROUPS AND THE MOLECULES OF BIOCHEMISTRY

  Publisher Summary

  This chapter discusses the most common functional groups of the two main types, such as groups with only covalent single bonds and groups that include covalent double bonds. It explains the nomenclature of compounds containing those groups. The chapter describes proteins, carbohydrates, lipids, and nucleic acids, which are the molecules of biochemistry. A functional group is an atom or group that bonds to one or more carbon atoms in an organic molecule and contributes a characteristic chemical behavior to the molecule. In organic compounds, the OH group is usually covalently bonded and is called the hydroxyl group. The attachment of a hydroxyl group to an aromatic ring gives a class of organic compounds known as phenols, ArOH. Replacement of the hydrogen atoms of an ammonia molecule by hydrocarbon groups gives amines. The carbonyl group consists of a carbon atom and an oxygen atom joined by a covalent double bond. An aldehyde, RCHO, is a compound in which a hydrogen atom and a hydrocarbon group are bonded to a carbonyl group. Ketones are used extensively as solvents, especially in lacquers. A carboxylic acid, RCOOH, has a functional group that is a combination of a carbonyl group and a hydroxyl group. The chapter explains the concept of infrared and ultraviolet spectroscopy.

  In this chapter the most common functional groups of the two main types—groups with only covalent single bonds and groups that include covalent double bonds—are discussed. The nomenclature of compounds containing these groups is explained. Examples are given of some simple compounds and some more complex compounds of specific interest containing each of the groups. A few of the most common preparations and reactions of the various types of compounds are included. The chapter (and the book) ends with a brief introduction to proteins, carbohydrates, lipids, and nucleic acids—the molecules of biochemistry.

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  eBook - ePub

  Reaction Mechanisms in Organic Chemistry

  • Metin Balcı(Author)
  • 2021(Publication Date)
  • Wiley-VCH

    (Publisher)

  5 Carbonyl Compounds

  The carbonyl group and its chemistry are a significant part of organic chemistry. Most biological and natural compounds contain carbonyl functionality. Particularly with the addition of heteroatoms to carbon–oxygen double bonds (C=O), some new functional groups can be designed. Condensation reactions that provide the formation of new carbon—carbon bonds play an essential role in carbonyl chemistry. The reactions of the carbonyl group can be perceived as very comprehensive and complicated at first. However, when the reactivity of the carbonyl group and the reaction mechanism are studied in depth, it is seen that almost all of these reactions occur via the same mechanism. For example, the commonly known condensation reactions (ester condensation, aldol condensation, Knoevenagel condensation, Perkin condensation, etc.) all proceed by the same mechanism. They are referred to by different names according to the starting compound used. If the characteristic features of these reactions are understood, it will be seen that carbonyl group chemistry is a straightforward and enjoyable subject.

  Before starting to examine the reactions of the carbonyl group, it is necessary to understand the reactivity of the carbonyl group. As discussed in previous sections, in order for a chemical reaction to occur, the polarization of bond electrons is required on one side of a molecule with a high electron density and a low electron density on the other. For example, in nucleophilic substitution reactions, we saw that carbon—halogen (C—X) bonds are polarized and nucleophiles attack the carbon atom.

  5.1 Reactivity of the Carbonyl Group

  The carbonyl group consists of a σ bond and a π bond between the carbon and the oxygen atom. The carbonyl carbon atom and the oxygen atom are sp2 -hybridized. Three atoms are connected to the carbonyl carbon atom. All those atoms lie in a plane and the bond angles are approximately 120°. The p orbitals perpendicular to this plane, one on carbon and the other on oxygen, form the π bond. The oxygen atom has two pairs of nonbonding electrons. They occupy the remaining sp2

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  eBook - ePub

  Introduction to Organic Geochemistry

  • Stephen D. Killops, Vanessa J. Killops(Authors)
  • 2013(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Table 2.1 .

  Table 2.1

  Geochemically important functional groups

  formula*	group/compound name
  R–OH	hydroxyl: alcohol (R = alkyl group) phenol (R = phenyl group)
  	carbonyl: aldehyde (R = H) ketone (R = alkyl or phenyl)
  	carboxyl: carboxylic acid (R = H) ester (R = alkyl group)
  —O—	ether
  —NH2	amine
  	amide
  —SH	thiol (or mercaptan)
  —S—	sulphide
  	alkene

  *R is used to represent aliphatic chains (alkyl groups) or aromatic rings. The latter can also be called aryl groups, and are sometimes represented by Ar.

  More than one type of functional group may be present in a molecule, as in amino acids, which contain both carboxylic acid and amino groups. Similarly, amides can be considered to comprise amino and carbonyl groups, and carboxylic acids to comprise carbonyl and hydroxyl groups, although the behaviour of each group is modified by the neighbouring group. The double bond of an alkene can also be thought of as a functional group.

  Heteroatoms can be incorporated into cyclic systems, and some of the geochemically important are shown in Table 2.2 .

  Table 2.2

  Geochemically important cyclic units

  formula	unit name
  	quinones (1, 2 and 1, 4) (i.e. 2 carbonyl groups within a cyclic system)

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  eBook - PDF

  Introduction to Genomic Signal Processing with Control

  • Aniruddha Datta, Edward R. Dougherty(Authors)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  2.2 Some Chemical Bonds and Groups Commonly En-countered in Biological Molecules C-H Compounds Compounds containing only carbon and hydrogen are called hydrocarbons . Examples are methane ( CH 4 ) and ethane ( C 2 H 6 ), which have the structures shown below. C H H H H Methane C H H H Methyl Group C C H H H H H C C H H H H H H Ethane Ethyl Group By removing one of the hydrogen atoms from methane, we obtain a highly reactive group called the methyl group . The ethyl group is similarly derived from ethane. C − O Compounds We next consider organic compounds that contain carbon and oxygen in addition to other elements. There are different classes of compounds that fall into this category. Alcohols are characterized by the presence of the hydroxyl (OH) group and have the general formula R − OH. Here R could be any organic group. When R = CH 3 , i.e. the methyl group, the corresponding alcohol is called methyl alcohol or methanol . When R = C 2 H 5 i.e. the ethyl group, the corresponding alcohol is called ethyl alcohol or ethanol . Aldehydes are characterized by the general formula 10 Introduction to Genomic Signal Processing with Control C H R O where R is any organic group. When R = H , the corresponding aldehyde is called formaldehyde and when R = CH 3 , the corresponding aldehyde is called acetaldehyde . Ketones are characterized by the general formula C R 2 O R 1 where R 1 and R 2 can be any two organic groups. The C = O (C double bonded with O) is called the carbonyl group and it is present in both aldehydes and ketones. Carboxylic Acids are characterized by the general formula C OH R O where R is any organic group. When R = H , the corresponding acid is called formic Acid while when R = CH 3 , the corresponding acid is called acetic Acid . The COOH group present in all carboxylic acids is called a Carboxyl Group.

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  eBook - PDF

  Organic Chemistry

  A Mechanistic Approach

  • Penny Chaloner(Author)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  4.15(c) Acetic acid—molecules are held together by hydrogen bonds. Key Points from Section 4.5 • All carbonyl compounds involve a polar carbon–oxygen double bond, and both atoms are sp 2 hybridized. The oxygen atom bears two lone pairs of electrons. • Aldehydes have a formula RC( =O)H (also written RCHO) and a nomenclature suffix -al. The carbonyl carbon atom is C-1. • Ketones have a formula R 2 C =O and a nomenclature suffix -one. The chain is numbered to give the carbonyl carbon atom the lowest number. • Acid derivatives include carboxylic acids, RC( =O)OH, suffix -oic acid, esters RC( =O)OR′ , suffix -oate; amides, R(C =O)NH 2 or RC( =O)NR 2 ′ , suffix, -amide, acid chlorides, RC( =O)Cl, suffix -oyl chloride; anhydrides RC( =O)OC( =O)R′ , suffix -oic anhydride. • All carbonyl compounds can act as hydrogen-bond acceptors. Carboxylic acids and amides are also excellent hydrogen-bond donors. 104 4.6 Priorities in Nomenclature 4.6 PRIORITIES IN NOMENCLATURE We have mostly so far looked at molecules containing just one functional group—but of course, many really interesting compounds contain more than one. We need to have a system that allows us to prioritize. If a molecule contains both a carboxylic acid and a ketone, do we name it as an acid or as a ketone? The IUPAC rules tell us to name it as an acid—so 4.62 is 4-oxoheptanoic acid. Table 4.4 summarizes the ordering of groups and how they are named when they are a substitu- ent on a molecule containing a higher priority group. In general, you will see that the more highly oxidized the functional group, the higher up the table it appears. There is neither any prospect, nor any need, to learn all the IUPAC rules in one go (they run to several volumes, and there are various classes we have not dealt with, because we will encounter them infrequently), and later chapters will give review problems to remind you of the way we name the molecules that chapter deals with.

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  eBook - ePub

  Pharmaceutical Chemistry E-Book

  • David G. Watson(Author)
  • 2011(Publication Date)
  • Churchill Livingstone

    (Publisher)

  Chapter 5 Oxygen- and sulphur-containing functional groups

  David G. Watson

  Chapter contents

  Introduction 77

  Monohydric alcohols 78

  Ethanol 78

  Other aliphatic alcohols 79

  Benzyl alcohol 79

  Diols and triols 79

  Polyols 80

  Some chemical properties of alcohols 81

  Loss of water 81

  Oxidation 81

  Phenols 81

  Esterification 86

  Ethers 88

  Aldehydes and ketones 89

  Carboxylic acids 91

  Salts of carboxylic acids 93

  Salts formed between amines and carboxylic acids 94

  Esters 94

  Chemical stability 95

  Enzymatic hydrolysis of esters 97

  The role of esters in modifying physicochemical properties of drugs 101

  Esters for improving drug absorption 101

  Esters for improving water solubility 102

  Esters used for sustained drug delivery 103

  Esters for improving drug acceptability and reducing side effects 103

  The role of esters in terminating drug action 105

  Participation of the ester group in drug action 105

  The ester linkage in polymeric drugs 107

  Esters in biological systems 108

  Phosphate esters in biology 108

  Introduction

  Oxygen in the most electronegative element found in biomolecules since fluorine does not occur naturally in biological compounds. Its high affinity for electrons means that unlike nitrogen it does not share its lone pairs with protons readily. Thus oxygen-containing groups tend to be less potent in conferring pharmacological activity. For example, dopamine differs from noradrenaline by lacking a hydroxyl group but they both have potent effects on the heart: remove the amine group and activity is totally abolished. This is really a generalisation, it is probably truer to say that where oxygen-containing groups play an important role in conferring pharmacological activity they have a very specifically targeted function. In contrast, the charged nitrogen atom exerts a more general effect and may affect a number of targets. This theme will be expanded later in the chapter. Water is the fundamental oxygen-containing biologically active substance and some of its unique properties have been discussed in Chapter 1

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  eBook - ePub

  Organic Chemistry

  An Acid-Base Approach, Third Edition

  • Michael B. Smith(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  δ+ unit. Because of this polarization the proton is acidic (Section 6.2.1). Ethanoic acid is also drawn as a ball-and-stick model.

  Figure 5.8

  Structure of ethanoic acid.

  Nomenclature for carboxylic acids identifies the longest continuous chain for the acid, which must contain the CO2 H unit. The carboxyl carbon is always C1 so it is omitted from the name. The suffix for carboxylic acids is -oic acid, and the word “acid” is separated from the first part of the name. Carboxylic acid nomenclature is first illustrated by the 8-carbon acid, octanoic acid. All substituents are assigned numbers based on C1 for the Carboxyl Group, as in 2,3,3,4,5-pentamethylheptanoic acid. Complex substituents are accommodated as with all other compounds, illustrated by 3-(1,1-dimethylbutyl)-4-ethyl-heptadecanoic acid. Note that the substituted butyl group (b) group precedes the ethyl group (e) in the 17-carbon chain.

  Naming a cyclic carboxylic acid in which a COOH unit is attached to a ring uses the same the protocol as aldehydes. The ring is named, followed by the term -carboxylic acid. One example is cyclohexanecarboxylic acid, where the carboxylic group is attached to the six-membered ring. Substituents are numbered relative to the point of attachment of the carbonyl carbon of the COOH unit, which is always 1, as in 1-ethyl-3-methylcyclopentanecarboxylic acid. A carboxylic acid with two COOH units is known as a dicarboxylic acid, or a dioic acid. The molecule HO2 C(CH2 )3 CO2 H, for example, could be named 1,5-pentanedioic acid but the two carbonyl units must be at the ends of the molecule to be carboxyl units, so the 1- and 5- are redundant. The name is just pentanedioc acid.

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