What Does it Mean to be Organic?
Organic chemistry is most often described as the study of the chemistry of carbon. To the individual with a more nuanced knowledge of chemistry, this definition may seem appropriate. To the beginner, it may be slightly misleading. Not at all carbon compounds are ogranic, including some well known ones such as carbon dioxide and carbon monoxide. A better definition would indicate that organic compounds feature carbon-hydrogen bonds, but are not strictly limited to carbon and hydrogen. A significant number of organic compounds also contain oxygen and nitogen, and often they are referred to as "CHON" compounds - an acronym made from the symbols of the component elements.
Alkanes are the simplest organic molecules and are strictly hydrocarbons. That is, they are made only of carbon-carbon and carbon-hydrogen bonds. No other elements and no multiple bonds are present in an alkane. The carbon chain among the alkanes can either be straight chained or branched. The nature of the carbon chain has a profound effect on certain physical properties of the alkane. Compounds classified as alkanes can not be classified under any of the other compound types featured on this page.
When a carbon chain features a carbon-carbon double bond, the compound can be classified as an alkene.
When a carbon chain features a carbon-carbon triple bond, the compound can be classified as an alkyne.
A compound that is an aldehyde has a carbon-oxygen double bond on the terminal carbon (end of the carbon chain). A formula that ends in -CHO is an indicator that the compound is an aldehyde. Names for aldehydes end in "-al" or "-aldehyde." Due to the polarity of the C-O bond, dipole-dipole intermolecular forces are common amongst aldehydes.
A ketone is a compound in which there is carbon-oxygen double bond on a non-terminal carbon (a carbon not on the ends of the carbon chain). Names of ketones end with the suffix "-one." Similar to aldehydes, because of the polarity of the C-O bond, dipole-dipole intermolecular forces are common amongst ketones.
When a hydroxyl group (-OH) is bonded to a carbon, it is classified as an alcohol. The number of R groups that are connected to the carbon that is bonded to the hydroxyl group defines the compound as either primary, secondary, or tertiary. The names of alcohols end in the suffix "-ol" while the formulas of alcohols contain the sequence "COH." The significant difference in electronegativity between the oxygen and hydrogen results in significant polarity in the hydroxyl functional group. As a result, hydrogen bonding is common between alcohols, carboxylic acids, and water.
A carboxyl group is a carbon double bonded to an oxygen while also single bonded to an -OH group. The carboxyl group terminates the carbon chain, and like aldehydes can only be located at the end of the carbon chain. Formulas of carboxylic acids contain the formula "-COOH" while names for carboxylic acids end with the phrase "-oic acid." The significant difference in electronegativity between the oxygen and hydrogen coupled with the polar C-O bond that neighbors it, the result is significant polarity in the carboxyl functional group. As a result, hydrogen bonding is common between alcohols, carboxylic acids, and water.
Ethers are compounds in which the carbon chain is interrupted with a R-O-R' single bond sequence. The R groups can be carbon chains of any length.
Esters are similar to carboxylic acids. They have a carbon that is double bonded to an oxygen and single bonded to another. Unlike the carboxylic acid, the single bonded oxygen does not connect to a hydrogen and terminate the chain. Rather, it connects to another R group - a carbon chain of any length.
Amines are compounds in which the carbon chain features carbon-nitrogen bonds. These bonds can be found on the carbon chain's branches, ends, or within the chain itself. The number of carbons that are bonded to the nitrogen is used to categorize the amine as either primary, secondary, or tertiary.
Melting and Boiling Points
Among compounds with the same number of carbons, the alcohol and carboxylic acid will always have the highest melting and boiling point, while the alkane will always be the lowest. The alcohols and carboxylic acids are hgih due to the presence of intermolecular forces - specifically hydrogen bonding. The attraction between neighboring molecules will be exceptionally strong due to the very electronegative oxygens in the carboxyl and hydroxyl groups attracting the hydrogens on those same functional groups of neighboring molecules. Aldehydes and ketones will exhibit lower melting and boiling points because of the weaker dipole-dipole interactions that exist. While not as strong as hydrogen bonding, the C=O bonds creates a moderate dipole that can attract C=O bonds of neighboring molecules. This attraction needs to be overcome to separate molecules and causes melting and boiling points to be higher than the alkanes, but lesser than the alcohols and alkanes. In alkanes, there is no attraction between molecules, so the only obstacles to separating them comes from the molecule's mass and branching.