Classification of Chemical Compounds

Organic Compounds

Hydrocarbons are further classified into alkanes, alkenes, alkynes, and aromatic hydrocarbons. Let us see some examples of each. Alkanes Alkanes are saturated hydrocarbons having single bonds between each pair of carbon atoms. The simplest alkane is methane, in which one carbon atom is linked with four atoms of hydrogen. Ethane comes next, and has two carbon atoms linked to each other by single covalent bonds. Alkanes are the least reactive hydrocarbons. The representation of alkanes is shown alongside. The general formula for alkanes is C_nH_2n+2, while the same for cyclic alkanes is C_nH_2n. Alkyl Group Alkyl refers to a substituent or functional group that is derived from an alkane. It is represented by R-. The simplest alkyl group is the methyl group (CH₃), which is obtained by removing one hydrogen atom from methane (CH₄). Since an alkyl group is obtained by removing one hydrogen atom from the parent alkane, the general formula for alkyl groups can be given as C_nH_2n+1. Similarly, we can derive alkyl groups from ethane, propane, butane, pentane, hexane, etc. The names of a few alkyl groups are given below. Alkenes Alkenes are hydrocarbons having at least one C=C double bond. The simplest alkene is ethene, in which two carbon atoms are linked with a double covalent bond. Alkenes exhibit cis-trans isomerism, and are more reactive than alkanes. The general formula for alkenes with a single double-bond is C_nH_2n, while the same for cyclic alkenes is C_nH_2n-2. Alkenes with more than one double bond, are known as polyenes. Alkynes Alkynes are hydrocarbons having at least one C≡C triple bond. The simplest alkyne is ethyne, in which two carbon atoms are linked with a triple covalent bond. Alkynes are the most reactive hydrocarbons. The general formula for alkynes is C_nH_2n-2, while the same for cyclic alkynes is C_nH_2n-4. Aromatic Hydrocarbons Also known as arenes, aromatic hydrocarbons are characterized by a six-carbon ring that has alternate C=C double bonds, separated by C-C single bonds. They are known as aromatic hydrocarbons because most of these compounds have a sweet scent. Benzene is the simplest of these compounds. There are two types of aromatic hydrocarbons: monocyclic aromatic hydrocarbons (MAH) and polycyclic aromatic hydrocarbons (PAH). Aryl Group Aryl refers to a substituent or functional group that is derived from an aromatic ring. It is represented by Ar. The simplest aryl group is the phenyl group (C₆H₅), which is obtained by removing one hydrogen atom from the benzene (C₆H₆) ring. Similarly, we can derive aryl groups from naphthalene, thiophene, durene, xylene, toluene, etc. The names of the aryl groups derived from toluene and xylene, are given below.

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There are many functional groups that contain one or more oxygen atoms. Given below is a list of such functional groups, along with examples of compounds under each. Hydroxyl Group The hydroxyl group is a functional group that consists of a hydrogen atom and an oxygen atom, linked together by a covalent bond. The anion (OH^-) is the hydroxide anion, in which the negative charge resides on the oxygen atom. The hydroxyl radical (HO) is the neutral form of the hydroxyl group. In organic chemistry, the hydroxyl group is the defining functional group in alcohols. The general formula for acyclic alcohols is C_nH_2n+1OH. Now, let us have a look at some examples of organic compounds with the hydroxyl group. Ethers Ethers are organic compounds that contain the ether group, which is identified as two alkyl or aryl groups connected by an oxygen atom. The general formula of ethers is R-O-R'. Depending on whether the alkyl or aryl groups on both sides of the oxygen atom, are similar or different, ethers are classified as simple (symmetrical) and mixed (asymmetrical). In simple ethers, both R and R' are the same, while in mixed ethers, R and R' are different alkyl or aryl groups. The simplest ether is dimethyl ether, in which two methyl groups are connected to an oxygen atom. Aldehydes An organic compound that contains a formyl group, is known as an aldehyde. The presence of a carbonyl center that is linked to a hydrogen atom on one side, and an R- group on the other, is what defines an aldehyde. The carbonyl center is a carbon atom that is linked to an oxygen atom by double covalent bonds. The general formula for aldehydes is R-CHO, where -CHO is the formyl group. Organic compounds that have two aldehyde groups are known as dialdehydes. An example of a dialdehyde is glyoxal. Ketones Ketones are a group of organic compounds that contain the carbonyl group bonded to two other carbon atoms. The general formula of ketones is RC(=O)R', where R and R' can be alkyl or aryl groups. The simplest ketone is propanone (C₃H₆O), commonly known as acetone. Ketones with one or more alpha-hydrogen atoms (hydrogen atom attached to the alpha carbon), exhibit a phenomenon known as the keto-enol tautomerism. Ketones are also classified as symmetrical and asymmetrical ketones, depending on the nature of the alkyl and aryl groups present. Carboxylic Acids Carboxylic acids are organic compounds with at least one carboxyl group. The carboxyl group consists of a carbonyl group (RR'C=O), and a hydroxyl group (R-O-H). It is represented as -COOH. The general formula for carboxylic acids is R-COOH. These are the most commonly occurring acids in organic chemistry. However, carboxylic acids are weak acids with strong odors. The simplest member of this group is methanoic acid, which is also known as formic acid. Acid Chlorides Acid chlorides are organic compounds that contain the functional group -CO-Cl in their structure. They are derived from carboxylic acids. The general formula for acid chlorides is RCOCl. The simplest acid chloride is acetyl chloride (CH₃COCl). Similarly, carboxylic acids can also react to form acid halides (bromides, iodides, etc). Acid chlorides are also known as acyl chlorides, and are highly reactive. They are used in the synthesis of acid anhydrides, esters, and amides. Esters In inorganic chemistry, alkalis react with acids to form salts. Similarly, in organic chemistry, hydroxyl compounds (alcohols and phenols) react with oxoacids (acids that contain oxygen) to form esters. Thus, esters are nothing but salts of alcohols and acids. The most common esters are those derived from carboxylic acids. The process by which carboxylic acids react with alcohols in the presence of hydrochloric or sulfuric acids, is termed as esterification. The reaction involves the replacement of the hydroxyl (OH) group of the acid with the alkoxy (R'O) group of the alcohol. Esters can also be formed from acid anhydrides, acyl chlorides, carboxylate salts, and other esters.

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These are compounds with a functional group that has nitrogen atoms in it, which includes amines, amides, and nitriles. Amines Amines are organic compounds that are derivatives of ammonia (NH₃), in which the hydrogen atoms of ammonia have been replaced by alkyl or aryl groups. Amines can be identified by the presence of a nitrogen atom with a lone pair of electrons. Amines that have an aromatic ring attached to the nitrogen atom are known as aromatic amines, while others are known as aliphatic amines. All amines are more basic, when compared to ammonia. Amines can be categorized into three classes, and these are as follows: Primary Amines In primary amines, one of the three hydrogen atoms in ammonia, is replaced by an alkyl or aryl group. Thus, primary amines can be aliphatic or aromatic. The general chemical formula for primary amines is RNH₂, and they are named as "alkylamine". Examples of aliphatic primary amines are methylamine, ethylamine, and propylamine, while an example of aromatic primary amines is phenylamine (aniline). Secondary Amines In secondary amines, two of the three hydrogen atoms in ammonia, are replaced by alkyl or aryl groups. The general formula for secondary amines is R₂NH, and they are named as "dialkylamine". Secondary amines can be cyclic. Examples of secondary aliphatic amines are dimethylamine, ethylmethylamine, and diethylamine, while an example of secondary aromatic amines is diphenylamine. Tertiary Amines In tertiary amines, all the three hydrogen atoms of ammonia, are replaced by alkyl or aryl groups. In other words, a tertiary amine has three hydrocarbon groups attached to the nitrogen atom. Tertiary amines can be cyclic. The general formula for tertiary amines is R₃N, and they are named as "trialkylamine". Examples are trimethylamine and triphenylamine. If all four hydrogen atoms of an ammonium ion are replaced with alkyl or aryl groups, then a quaternary ammonium salt is formed, which is ionic. The simplest example of such a salt is tetramethylammonium chloride (CH₃)₄N⁺ Cl^-. Given below are a few examples of primary, secondary, and tertiary amines. Amides Amides or acid amides are carboxylic acid (RCOOH) derivatives, in which the -OH part of the acid is replaced by -NH₂ group. The general formula for organic amides is RCONH₂. Amides are further classified into primary, secondary and tertiary amides, based on the number of hydrogen atoms attached to the nitrogen atom of the functional group -CONH₂. Given below are a few examples of amides. Nitriles: Any organic compound that has a -C≡N functional group, is a nitrile. The term cyano is also used as a substituent prefix for nitriles. The general chemical formula for nitriles is RC≡N. Inorganic compounds that have the -C≡N group are known as cyanides. Nitriles are synthesized from hydrocarbons, cyanide salts, organic halides, amides, and oximes. The nomenclature of nitriles is on the basis of the number of carbon atoms in the longest carbon chain, including the carbon atom of the -C≡N group. Examples of simple nitriles are ethanenitrile, propanenitrile, and butanenitrile. Given below are a few examples of nitriles.

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Inorganic Compounds

Ionic compounds are compounds that contain one metal ion and one or more non-metal ions. Ionic compounds can be binary or ternary, and these two types are explained below, along with examples for each. Binary Ionic Compounds Ionic compounds that contain two elements, of which one is a metal and the other is a non-metal, are known as binary ionic compounds. One example of such a compound is sodium chloride (NaCl), which contains one sodium ion (metal) and one chloride ion (non-metal). More examples of binary ionic compounds are given below. Ternary Ionic Compounds Ionic compounds that contain three elements, which consist of at least one metal and one non-metal, are known as ternary ionic compounds. One example of such a compound is calcium carbonate (CaCO₃), which has one calcium ion (metal), one carbon ion (non-metal), and three oxygen ions. More examples of ternary ionic compounds are given below.

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Molecular compounds are compounds in which two or more non-metal atoms form a molecule. These are also known as covalent compounds because the bonds between the atoms in the molecule are covalent bonds. Molecular compounds may be polar or non-polar, depending on the shape of the molecule, and the polarity of the bonds formed between the constituent atoms. Here are some examples of molecular compounds.

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The term aqueous is used for the solution of a substance in water. Thus, aqueous acids are acids in solution with water. These acids are either binary acids or ternary acids. Let's have a look at the examples of each. Binary Acids Binary acids contain two elements, of which one is hydrogen, and the other one is a non-metal. One example is hydrochloric acid (HCl), which contains one hydrogen atom and one chlorine atom (non-metal). More examples of binary aqueous acids are given below. Ternary Acids Ternary acids contain three elements, of which one is hydrogen, one is oxygen, and the third element is a non-metal. One example is sulfuric acid (H₂SO₄), which contains hydrogen, sulfur (non-metal), and oxygen. More examples of ternary aqueous acids are given below.