Organic compounds have some very peculiar characteristics and properties when it comes to the kind of chemical reactions they undergo. Since organic compounds have very wide applications in the chemical and pharmaceutical industries, there ability to go into reactions and form other compounds and mixtures is of immense interest to chemists and chemical engineers. We shall discuss the 6 most important characteristics and features of organic compounds and how these characteristics affects the reactions they undergo.
Covalent Nature: Carbon atoms form stable covalent bonds with one another. A carbon-carbon single covalent bond has energy of 346 kJ mol-1. This high energy indicates a strong bond. Most organic compounds are stable because of the strong carbon-carbon bonds. Since they have a covalent nature, they do not ionize in solution and are non-conductors of electricity.
Polarity and Solubility of Non Polar Compounds:Carbon-hydrogen bonds are, non-polar, like the carbon-carbon bonds. This is because of the almost equal electronegativities of the two elements. Most organic compounds are non-polar unless the compounds consist of very electronegative elements like chlorine or groups like the hydroxyl group.
Since most organic compounds are non-polar, they cannot form bonds with water molecules. So most organic compounds are insoluble in water. For example, petrol, kerosene and paraffin oil do not dissolve in water. If an organic compound contains polar groups, hydrogen bonds can form between the polar groups in the molecules of the organic compound and the water molecules. This enables the compound to dissolve in water. For example, an ethanol molecule contains a hydroxyl group which is polar, so it is soluble in water.
Non-polar substances are held together only by weak intermolecular forces such as the Van der Waals forces, and so they can intermingle easily. This is why most organic compounds dissolve only in non-polar solvents like benzene or ether.
Low Melting and Boiling Points: Organic compounds generally have lower melting and boiling points than inorganic compounds. This is because these compounds possess relatively weak intermolecular bonds which can be easily broken by heat energy. Many of them (mainly those with low relative molecular masses) tend to be volatile and boil at temperatures below 300oC.
Thermal Instability:Many organic compounds are thermally unstable, decomposing into simpler molecules when heated to temperatures above 500oC. however, this property is sometimes of commercial importance as in the cracking of petroleum. This property is very useful in the fractional distillation of crude oil.
Flammability: Most of these compounds are flammable and born exothermically in a plentiful supply of air to yield carbon(IV) oxide and water. Thus, most fuels such as wood, coal, oil, petrol and natural gas are organic and their combustion provides our main source of heat energy.
Reactivity: Reactions involving these compounds tend to be much slower than the ionic reactions commonly encountered in inorganic chemistry. They usually require heating, thoroughly mixing and catalyst to speed up the reaction.
Characteristics of organic compounds include physical and chemical properties. Physical properties are observable and measurable, while chemical properties are the result of specific reaction pathways.
The covalent nature of carbon-carbon bonds makes them nonpolar and insoluble in water. This means that they cannot be separated by simple chemical methods. Hence they are usually distinguished by physical properties like boiling point, melting point, odor and index of refraction.
Type of Bonds in Organic Compounds
In organic compounds, carbon forms covalent bonds with other atoms. These bonds may be polar or non-polar. Polar chemical bonding involves the sharing of a pair of electrons between atoms, leading to the formation of a molecule. Non-polar chemical bonding does not involve the sharing of a pair of electrons, but rather atoms share some of their valence electrons with other atoms in the molecule.
Covalent bonding in organic compounds can be viewed by drawing Lewis structures or structural formulas, which give the kind and number of atoms in a molecule as well as their arrangement and how they are linked by covalent bonds. A covalent bond is indicated by a dash in a Lewis structure. In addition, atoms that have gained or lost a pair of valence electrons can be shown by dot diagrams.
Organic compounds often have lower melting and boiling points than inorganic substances. This is because the bonds in organic molecules are weaker, resulting in less binding energy. Many organic compounds also have low molecular masses, causing them to be volatile and to sublime at very low temperatures.
The atoms of organic compounds are typically not metals, so they cannot form metallic bonds. However, the atoms can form hydrogen bonds with other atoms in the molecule. This gives the molecule the properties of water, such as its vapor pressure and low melting point.
Examples of Organic Compounds
The four organic compounds vital to living organisms – carbohydrates, lipids, proteins and nucleic acids – are all built on carbon molecules. These molecules are the basis for chemical reactions within plant and animal cells, which enable them to find food, replicate and carry out all other life-related activities.
The chemistry of organic compounds is mainly the result of different bonds between carbon and other elements. These are called covalent bonds. The carbon atoms in organic molecules are almost always bound to hydrogen, but nitrogen and oxygen are also found in some organic compounds. These are called heteroatom-containing compounds, and they have a broad range of properties.
In general, the valence electrons in organic compounds are in orbitals with higher energy levels than those in inorganic substances. This gives them a greater affinity for electrons in other orbitals, enabling them to form bonds with them. This is why they are able to form complex and long chains of atoms, giving rise to organic molecules.
A useful way of classifying organic compounds is to look at the functional groups they contain. For example, the hydroxyl group -OH, aldehyde group -CHO and carboxylic acid group -COOH are common functional groups in organic molecules, and their presence gives them characteristic chemical properties. Most organic compounds are hydrophobic, meaning they are insoluble in water. However, some, such as low molecular weight alcohols, amines and carboxylic acids, have polar groups that can form hydrogen bonds with water molecules, making them soluble in water.
Electronic Structure of Organic Compounds
Carbon, which is present in all organic compounds, has four electrons in its outer shell. This makes it a tetravalent atom, capable of combining with other atoms by covalent bonds. It also has the ability to form cyclic structures, which can have single, double or triple bonds. These characteristics make it suitable for forming organic molecules.
Inorganic substances, on the other hand, have stronger non-covalent interactions. As such, they tend to stay together and are unable to dissolve easily in non-polar solvents like water. They are a poor conductor of electricity and generally have low melting and boiling points.
The simplest organic molecules are linear hydrocarbons, such as the gas ethane, which has a molecular formula of C2H6. A simple structural formula, which shows the arrangement of bonds in a molecule, can be drawn using line-angle symbols or a structure table. These symbols convey very little three-dimensional information, however, and a more sophisticated way to represent the bonding pattern of an organic molecule is through molecular diagrams or a structural formula.
The IUPAC nomenclature system for organic compounds uses root names to indicate the length of the longest carbon chain, prefixes and suffixes to show the type of structure, and symbols for carbon-carbon bonds. The configuration of these bonds defines whether a compound is aliphatic, aromatic or cyclic, as well as whether it is saturated or unsaturated. It is also possible to classify organic compounds by the presence of functional groups, which are sites of comparatively high reactivity.
Configuration of Organic Compounds
Organic compounds are based on carbon and almost always bonded to hydrogen. They can be straight-chain, branched-chain, or cyclic. They may also contain functional groups that influence their properties. Some of the most common examples are alcohols, carboxylic acids, and amines. The reactivity of these groups determines their properties. Some organic compounds are polar and others are nonpolar. They can be either liquids or solids, and are soluble in organic solvents. Some of them are volatile, and some are toxic. Others are insoluble in water, and some have a high molecular weight.
A molecule with two possible enantiomers can be represented by Fischer projection formulae, which display the absolute configuration of the asymmetric carbon atoms in each of the two isomers. Alternatively, the relative configuration can be assigned by chemical correlation using a reference compound with known absolute configuration. This method requires the use of chiral auxiliary and careful selection of the right-handed and left-handed enantiomers.
The relative configuration of a molecule can also be established by comparing the rotational spectra of one molecule with that of another molecule with a different absolute configuration. The most commonly used labeling system uses the letters R and S to indicate the absolute configuration of a molecule. This is based on the priority rules of Cahn, Ingold, and Prelog. These rules are based on the relative importance of the groups attached to the asymmetric carbon atom.