Name the Family to Which Each Organic Compound Belongs. The First Answer Has Been Filled in for You.

3.ane: Functional Groups

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Objectives

After completing this section, you should be able to

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

Key Terms

Brand certain that you can define, and utilize in context, the key term below.

• functional group

Study Notes

The concept of functional groups is a very important one. We wait that you will need to refer back to tables at the end of Department 3.i quite frequently at first, as information technology is not really viable to larn the names and structures of all the functional groups and compound types at one sitting. Gradually they will go familiar, and eventually you volition recognize them automatically.

Functional groups are small groups of atoms that exhibit a characteristic reactivity. A particular functional grouping will most always brandish its distinctive chemical behavior when it is present in a chemical compound. Considering of their importance in understanding organic chemistry, functional groups accept specific names that often bear over in the naming of individual compounds incorporating the groups.

As we progress in our written report of organic chemistry, it will get extremely important to be able to apace recognize the most common functional groups, because they are the key structural elements that define how organic molecules react. For at present, we will but worry nigh cartoon and recognizing each functional group, as depicted by Lewis and line structures. Much of the rest of your study of organic chemistry volition be taken up with learning nearly how the different functional groups tend to bear in organic reactions.

Drawing abbreviated organic structures

Oft when cartoon organic structures, chemists observe it convenient to use the letter 'R' to designate part of a molecule exterior of the region of involvement. If we simply want to refer in general to a functional group without drawing a specific molecule, for example, we can employ 'R groups' to focus attending on the group of interest:

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

Common Functional Groups

In the following sections, many of the common functional groups plant in organic chemistry volition 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 often ignored when listing functional groups) is chosen an alkane series, characterized past single bonds between two carbons and between carbon and hydrogen. Some examples of alkanes include methyl hydride, CH₄, is the natural gas you lot may burn in your furnace or on a stove. Octane, C_eightH₁₈, is a component of gasoline.

Alkanes

Alkenes (sometimes called olefins) have carbon-carbon double bonds, and alkynes take carbon-carbon triple bonds. Ethene, the simplest alkene example, is a gas that serves every bit a cellular signal in fruits to stimulate ripening. (If you want bananas to ripen speedily, put them in a paper pocketbook along with an apple tree - the apple emits ethene gas, setting off the ripening process in the bananas). Ethyne, commonly chosen acetylene, is used every bit 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 have linear geometry (due to sp hybrid orbitals at the alkyne carbons). Furthermore, many alkenes tin can take 2 geometric forms: cis or trans (or Z and E which will be explained in detail in Chapter seven). The cis and trans forms of a given alkene are different molecules with different physical properties in that location is a very high free energy barrier to rotation most a double bond. In the example beneath, the divergence between cis and trans alkenes is readily apparent.

Alkanes, alkenes, and alkynes are all classified as 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 as unsaturated hydrocarbons. As we will see in Chapter seven, hydrogen can be added to double and triple bonds, in a type of reaction called 'hydrogenation'.

The effluvious 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 compound with a distinctive 'mothball' smell. Aromatic groups are planar (flat) band structures, and are widespread in nature. We volition learn more about the construction and reactions of aromatic groups in Chapter fifteen.

Aromatics

Functional Groups with Carbon Single Bonds to other Atoms

Halides

When the carbon of an paraffin is bonded to ane 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 past X due to the similar chemical science of halogens. Chloroform is a useful solvent in the laboratory, and was one of the before anesthetic drugs used in surgery. Chlorodifluoromethane was used as a refrigerant and in droplets sprays until the late twentieth century, only its utilize was discontinued after it was found to accept 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 group, a carbon is single-bonded to an OH group (the OH group, past itself, is referred to as a hydroxyl). Except for methanol, all alcohols can be classified as main, secondary, or tertiary. In a primary alcohol, the carbon bonded to the OH group is as well bonded to simply ane other carbon. In a secondary alcohol and 3rd alcohol, the carbon is bonded to 2 or three other carbons, respectively. When the hydroxyl group is directly fastened to an aromatic ring, the resulting grouping is chosen 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 grouping, a central oxygen is bonded to two carbons. Below are the line and Lewis structures of diethyl ether, a common laboratory solvent and as well one of the start medical amazement agents.

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

Amines

Amines are characterized past nitrogen atoms with single bonds to hydrogen and carbon. Simply as in that location are chief, secondary, and tertiary alcohols, there are principal, secondary, and third amines. Ammonia is a special case with no carbon atoms.

One of the most important backdrop of amines is that they are basic, and are readily protonated to class ammonium cations. In the instance where a nitrogen has four bonds to carbon (which is somewhat unusual in biomolecules), it is called a 4th ammonium ion.

Note: Do not be confused by how the terms 'main', 'secondary', and 'tertiary' are applied to alcohols and amines - the definitions are different. 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 commonly referred to as a carbonyl. Ketones and aldehydes are two closely related carbonyl-based functional groups that react in very similar ways. In a ketone, the carbon cantlet 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 two hydrogens.

Carboxylic acids and acid 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 i of the halogens), the functional grouping is considered to be one of the 'carboxylic acid derivatives', a designation that describes a grouping of several functional groups. The eponymous member of this grouping is the carboxylic acid functional group, in which the carbonyl is bonded to a hydroxyl (OH) group.

As the proper noun implies, carboxylic acids are acidic, meaning that they are readily deprotonated to form the conjugate base of operations form, called a carboxylate (much more about carboxylic acids in Chapter twenty).

In amides, the carbonyl carbon is bonded to a nitrogen. The nitrogen in an amide can exist bonded either to hydrogens, to carbons, or to both. Some other mode 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 some other carbon. Another manner of thinking of an ester is that it 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, in that location are two carbonyl carbons with an oxygen in between. An acid anhydride is formed from combination of 2 carboxylic acids with the loss of water (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 grouping, a carbon is triple-bonded to a nitrogen. Nitriles are too often referred to as cyano groups.

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

Phosphates

Phosphorus is a very of import element in biological organic chemistry, and is found equally the central atom in the phosphate group. Many biological organic molecules incorporate phosphate, diphosphate, and triphosphate groups, which are linked to a carbon atom by the phosphate ester functionality.

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

Molecules with Multiple Functional Groups

A unmarried compound may comprise several dissimilar functional groups. The six-carbon saccharide molecules glucose and fructose, for example, comprise aldehyde and ketone groups, respectively, and both contain five alcohol groups (a chemical compound with several alcohol groups is often referred to equally a 'polyol').

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

The male 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 complete list, this section has covered nigh of the important functional groups that nosotros will encounter in biological and laboratory organic chemistry. The table found below provides a summary of all of the groups listed in this section, plus a few more that will be introduced later on in the text.

Practice \(\PageIndex{1}\)

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

Reply

a) carboxylate, sulfide, aromatic, two amide groups (one of which is cyclic)

b) third alcohol, thioester

c) carboxylate, ketone

d) ether, principal amine, alkene

two: Draw one example each (there are many possible right answers) of compounds fitting the descriptions below, using line structures. Be sure to designate the location of all non-zero formal charges. All atoms should accept complete octets (phosphorus may exceed the octet rule).

a) a compound with molecular formula C₆H₁₁NO that includes alkene, secondary amine, and primary alcohol functional groups

b) an ion with molecular formula C₃H₅O_half-dozenP ^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 group.

Functional Grouping Tables

Exercises

Questions

Q3.1.1

The following is the molecule for ATP, or the molecule responsible for energy in human cells. Identify the functional groups for ATP.

Solutions

S3.1.one

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Source: https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(McMurry)/03%3A_Organic_Compounds-_Alkanes_and_Their_Stereochemistry/3.01%3A_Functional_Groups