231 Introduction to Functional Groups Section Review Answers

3.2: Functional Groups

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Objectives

Later on completing this department, you should be able to

1. explain why the backdrop of a given organic compound are largely dependent on the functional grouping or groups present in the chemical compound.
2. place the functional groups present in each of the following compound types: alkenes, alkynes, arenes, (alkyl and aryl) halides, alcohols, ethers, aldehydes, ketones, esters, carboxylic acids, (carboxylic) acrid chlorides, amides, amines, nitriles, nitro compounds, sulfides and sulfoxides.
3. place the functional groups present in an organic compound, given its structure.
4. Given the structure of an organic chemical compound containing a single functional group, identify which of the chemical compound types listed under Objective 2, above, it belongs to.
5. draw the structure of a elementary example of each of the compound types listed in Objective 2.

Key Terms

Make certain that you tin can define, and use in context, the key term below.

• functional group

Written report Notes

The concept of functional groups is a very important one. Nosotros expect that you lot will demand to refer back to tables at the end of Section 3.1 quite frequently at first, as it is non really viable to acquire the names and structures of all the functional groups and chemical compound types at 1 sitting. Gradually they will get familiar, and eventually you will recognize them automatically.

Functional groups are pocket-size groups of atoms that exhibit a feature reactivity. A particular functional group will well-nigh always display its distinctive chemic behavior when it is present in a chemical compound. Because of their importance in agreement organic chemical science, functional groups have specific names that often deport over in the naming of private compounds incorporating the groups.

As nosotros progress in our study of organic chemistry, it will become extremely important to be able to quickly recognize the most mutual functional groups, because they are the key structural elements that define how organic molecules react. For now, we volition only worry about cartoon and recognizing each functional group, equally depicted by Lewis and line structures. Much of the residual of your written report of organic chemical science will exist taken up with learning about how the different functional groups tend to behave in organic reactions.

Drawing abbreviated organic structures

Often when drawing organic structures, chemists find it convenient to utilise the alphabetic character 'R' to designate part of a molecule outside of the region of involvement. If we just want to refer in general to a functional grouping without drawing a specific molecule, for example, we can apply 'R groups' to focus attending on the group of interest:

The 'R' group is a convenient way to abridge the structures of large biological molecules, especially when we are interested in something that is occurring specifically at 1 location on the molecule.

Common Functional Groups

In the following sections, many of the common functional groups plant in organic chemistry will be described. Tables of these functional groups can be found at the bottom of the page.

Hydrocarbons

The simplest functional group in organic chemistry (which is ofttimes ignored when listing functional groups) is called an alkane, characterized by single bonds between ii carbons and between carbon and hydrogen. Some examples of alkanes include methane, CH_four, is the natural gas you lot may burn in your furnace or on a stove. Octane, C₈H₁₈, is a component of gasoline.

Alkanes

Alkenes (sometimes called olefins) have carbon-carbon double bonds, and alkynes have carbon-carbon triple bonds. Ethene, the simplest alkene example, is a gas that serves as a cellular betoken in fruits to stimulate ripening. (If you want bananas to ripen chop-chop, put them in a paper purse along with an apple - the apple emits ethene gas, setting off the ripening process in the bananas). Ethyne, commonly called acetylene, is used equally a fuel in welding blow torches.

Alkenes and alkynes

Alkenes have trigonal planar electron geometry (due to sp² hybrid orbitals at the alkene carbons) while alkynes take linear geometry (due to sp hybrid orbitals at the alkyne carbons). Furthermore, many alkenes can take ii geometric forms: cis or trans (or Z and E which will be explained in particular in Affiliate 7). The cis and trans forms of a given alkene are different molecules with dissimilar physical backdrop there is a very high energy barrier to rotation about a double bond. In the case below, the deviation between cis and trans alkenes is readily credible.

Alkanes, alkenes, and alkynes are all classified every bit hydrocarbons, because they are composed solely of carbon and hydrogen atoms. Alkanes are said to be saturated hydrocarbons, because the carbons are bonded to the maximum possible number of hydrogens - in other words, they are saturated with hydrogen atoms. The double and triple-bonded carbons in alkenes and alkynes have fewer hydrogen atoms bonded to them - they are thus referred to every bit unsaturated hydrocarbons. As nosotros will run into in Chapter seven, hydrogen tin can be added to double and triple bonds, in a type of reaction called 'hydrogenation'.

The aromatic group is exemplified by benzene (which used to be a commonly used solvent on the organic lab, but which was shown to be carcinogenic), and naphthalene, a chemical compound with a distinctive 'mothball' smell. Aromatic groups are planar (flat) band structures, and are widespread in nature. Nosotros volition larn more virtually the construction and reactions of aromatic groups in Chapter fifteen.

Aromatics

Functional Groups with Carbon Unmarried Bonds to other Atoms

Halides

When the carbon of an alkane is bonded to one or more halogens, the group is referred to as a alkyl halide or haloalkane. The presence of a halogen atom (F, Cl, Br, or I), is often represented by X due to the like chemistry of halogens. Chloroform is a useful solvent in the laboratory, and was one of the before anesthetic drugs used in surgery. Chlorodifluoromethane was used equally a refrigerant and in aerosol sprays until the late twentieth century, only its use was discontinued afterwards information technology was found to have harmful effects on the ozone layer. Bromoethane is a simple alkyl halide often used in organic synthesis. Alkyl halides groups are quite rare in biomolecules.

Alcohols and Thiols

In the alcohol functional grouping, a carbon is single-bonded to an OH grouping (the OH group, by itself, is referred to equally a hydroxyl). Except for methanol, all alcohols can be classified every bit primary, secondary, or 3rd. In a primary alcohol, the carbon bonded to the OH group is also bonded to only one other carbon. In a secondary alcohol and tertiary alcohol, the carbon is bonded to two or three other carbons, respectively. When the hydroxyl grouping is directly attached to an aromatic ring, the resulting grouping is called a phenol.

The sulfur analog of an alcohol is called a thiol (the prefix thio, derived from the Greek, refers to sulfur).

Ethers and sulfides

In an ether functional group, a central oxygen is bonded to ii carbons. Beneath are the line and Lewis structures of diethyl ether, a common laboratory solvent and as well i of the first medical anaesthesia agents.

In sulfides, the oxygen atom of an ether has been replaced by a sulfur atom.

Amines

Amines are characterized by nitrogen atoms with single bonds to hydrogen and carbon. Just as there are principal, secondary, and 3rd alcohols, at that place are primary, secondary, and tertiary amines. Ammonia is a special example with no carbon atoms.

Ane of the most important properties of amines is that they are bones, and are readily protonated to form ammonium cations. In the instance where a nitrogen has iv bonds to carbon (which is somewhat unusual in biomolecules), it is chosen a quaternary ammonium ion.

Note: Do not be confused by how the terms 'primary', 'secondary', and 'tertiary' are applied to alcohols and amines - the definitions are dissimilar. In alcohols, what matters is how many other carbons the alcohol carbon is bonded to, while in amines, what matters is how many carbons the nitrogen is bonded to.

Carbonyl Containing Functional Groups

Aldehydes and Ketones

There are a number of functional groups that comprise a carbon-oxygen double bond, which is ordinarily referred to as a carbonyl. Ketones and aldehydes are two closely related carbonyl-based functional groups that react in very like means. In a ketone, the carbon atom of a carbonyl is bonded to two other carbons. In an aldehyde, the carbonyl carbon is bonded on 1 side to a hydrogen, and on the other side to a carbon. The exception to this definition is formaldehyde, in which the carbonyl carbon has bonds to 2 hydrogens.

Carboxylic acids and acrid derivatives

If a carbonyl carbon is bonded on one side to a carbon (or hydrogen) and on the other side to a heteroatom (in organic chemistry, this term generally refers to oxygen, nitrogen, sulfur, or one of the halogens), the functional group is considered to be one of the 'carboxylic acid derivatives', a designation that describes a grouping of several functional groups. The eponymous fellow member of this grouping is the carboxylic acid functional grouping, in which the carbonyl is bonded to a hydroxyl (OH) group.

Equally the proper noun implies, carboxylic acids are acidic, pregnant that they are readily deprotonated to form the cohabit base form, chosen a carboxylate (much more nigh carboxylic acids in Affiliate 20).

In amides, the carbonyl carbon is bonded to a nitrogen. The nitrogen in an amide tin exist bonded either to hydrogens, to carbons, or to both. Another fashion of thinking of an amide is that it is a carbonyl bonded to an amine.

In esters, the carbonyl carbon is bonded to an oxygen which is itself bonded to another carbon. Another way of thinking of an ester is that information technology is a carbonyl bonded to an alcohol. Thioesters are similar to esters, except a sulfur is in place of the oxygen.

In an acid anhydride, there are two carbonyl carbons with an oxygen in between. An acid anhydride is formed from combination of two carboxylic acids with the loss of h2o (anhydride).

In an acyl phosphate, the carbonyl carbon is bonded to the oxygen of a phosphate, and in an acid chloride, the carbonyl carbon is bonded to a chlorine.

Nitriles and Imines

In a nitrile group, a carbon is triple-bonded to a nitrogen. Nitriles are also often referred to as cyano groups.

Molecules with carbon-nitrogen double bonds are called imines, or Schiff bases.

Phosphates

Phosphorus is a very important chemical element in biological organic chemistry, and is plant as the fundamental atom in the phosphate group. Many biological organic molecules contain phosphate, diphosphate, and triphosphate groups, which are linked to a carbon atom by the phosphate ester functionality.

Because phosphates are so abundant in biological organic chemistry, it is convenient to draw them with the abbreviation 'P'. Notice that this 'P' abridgement includes the oxygen atoms and negative charges associated with the phosphate groups.

Molecules with Multiple Functional Groups

A single compound may incorporate several unlike functional groups. The six-carbon sugar molecules glucose and fructose, for case, incorporate aldehyde and ketone groups, respectively, and both incorporate five alcohol groups (a compound with several booze groups is often referred to as a 'polyol').

Capsaicin, the compound responsible for the heat in hot peppers, contains phenol, ether, amide, and alkene functional groups.

The male person sex hormone testosterone contains ketone, alkene, and secondary alcohol groups, while acetylsalicylic acid (aspirin) contains aromatic, carboxylic acid, and ester groups.

While not in any way a consummate list, this section has covered most of the important functional groups that we volition meet in biological and laboratory organic chemistry. The table plant below provides a summary of all of the groups listed in this department, plus a few more that will be introduced subsequently in the text.

Practise \(\PageIndex{1}\)

Identify the functional groups in the following organic compounds. Country whether alcohols and amines are primary, secondary, or tertiary.

Answer

a) carboxylate, sulfide, effluvious, ii amide groups (1 of which is circadian)

b) tertiary alcohol, thioester

c) carboxylate, ketone

d) ether, primary amine, alkene

2: Draw i example each (there are many possible correct answers) of compounds fitting the descriptions below, using line structures. Be certain to designate the location of all non-zero formal charges. All atoms should have complete octets (phosphorus may exceed the octet dominion).

a) a compound with molecular formula C_half-dozenH₁₁NO that includes alkene, secondary amine, and chief alcohol functional groups

b) an ion with molecular formula C₃H₅O₆P ^2- that includes aldehyde, secondary alcohol, and phosphate functional groups.

c) A compound with molecular formula C₆H₉NO that has an amide functional group, and does not have an alkene grouping.

Functional Group Tables

Exercises

Questions

Q3.1.1

The post-obit is the molecule for ATP, or the molecule responsible for free energy in human being cells. Place the functional groups for ATP.

Solutions

S3.1.1

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