HYDRCARBNS AND THEIR DERIVATIVES The field of organic chemistry includes the study of hydrocarbons (compounds composed of carbon and hydrogen atoms covalently bonded together) and their derivatives (variations of hydrocarbons, usually involving other atoms such as oxygen, nitrogen, and halogens). Carbon is only the fifteenth most common element, acounting for a very modest 0.048 percent of the Earth's crust, but we would be lost without it. What sets the carbon atom apart is that it is the party animal of the atomic world, latching on to many other atoms (including itself) and holding tight, forming molecular conga lines of hearty robustness the very trick of nature necessary to build proteins and DNA. As Paul Davies has written: If it wasn't for carbon, life as we know it would be impossible. Probably any sort of life would be impossible. Yet carbon is not all that plentiful even in humans, who so vitally depend on it. f every 200 atoms in your body, 126 are hydrogen, 51 are oxygen, and just 19 are cabon. Bill Bryson, A Short History of Nearly Everything (2003) I. Classifications of Hydrocarbons and IUPAC Nomenclature The International Union of Pure and Applied Chemistry has developed a system of rules for naming organic molecules. Rule #1: Find the longest unbroken chain of carbons and use that as the main name of the compound. The following list gives prefixes used to identify the number of carbons in the longest chain. 1 meth 6 hex 2 eth 7 hept 3 prop 8 oct 4 but 9 non 5 pent 10 dec A. Alkanes: hydrocarbons containing all carbon-carbon single bonds. The general formula for an alkane is C n H 2n+2. To name these hydrocarbons, add the ending -ane to the appropriate prefix. Hydrogens do not need to be drawn in on the structural formulas. C 6 H 14 (molecular formula) C C C C C C hexane (structural formula) (IUPAC name) B. Alkenes: hydrocarbons containing one or more carbon-carbon double bond. The general formula for an alkene is C n H 2n. To name these hydrocarbons, the longest chain must include the double bond(s) and the ending -ene is added on after the correct prefix.
Rule #2: To name isomers, number the carbons of the chain making sure that the double (or triple) bond has the smallest possible number. The number one (1) does not need to be written, it is understood. C 3 H 6 C 4 H 8 C 4 H 8 C = C C C = C C C C C = C C propene butene 2-butene C. Alkynes: hydrocarbons containing one or more carbon-carbon triple bonds. The general formula for an alkyne is C n H 2n-2. To name these hydrocarbons, the longest chain must include the triple bond(s) and the ending -yne is added on after the correct prefix. C 2 H 2 ethyne D. Cyclic Compounds: the carbon chain forms a ring structure. The simplest cyclic compound must contain at least 3 carbons. To name these compounds, the term cyclo- is added at the beginning of the correct name of the compound if it had been a straight chain. E. Alkyl Substituents: a hydrocarbon branch off of a longer main hydrocarbon chain. Rule #3: In naming, locate and number the carbons on the longest chain, then name and number the substituent (giving it the lowest number possible), changing the -ane ending to -yl. C C C C C C C C C 2 methyloctane F. Dienes and Trienes: hydrocarbons and cyclic hydrocarbons having two (di-) or three (tri-) C-C double bonds. In naming these, number the double bonds according to the lowest numbering possible, then also include the correct prefix before the -ene ending. C = C C = C C C C = C = C = C C C C = C C = C 1,3-hexadiene 1,2,3-hexatriene 1,3-cyclobutadiene
G. Halogen Substituents: locate and number a halogen substituent, as always giving the substituent the lowest number possible, replace the -ine ending of the halogen with -o. Rule #4: If more than one halo- or alkyl- substituent is present, number them as low as possible, but name them in alphabetical rather than numerical order. F Br C C C C 3 bromo 1 fluorobutane Rule #5: If you have more than one of the same type of substituent use the prefixes di- (meaning 2), tri- (meaning 3). F F C C C C C C 1,3 difluorohexane II. Functional Groups and Their Nomenclature A functional group is the different area on a hydrocarbon, and usually includes other elements than just carbon and hydrogen. A. Alcohols - H The functional group that makes a molecule an alcohol is the - H group. While CH 4 is called methane, CH 3 H is called methyl alcohol or methanol. In naming, locate the longest carbon chain containing the functional group, give the alcohol carbon the lowest number possible, and replace the -e ending of the alkane with -ol, as in methanol. H H C H H methanol C C C C C H H 1,3 pentadiol (get it?)
B. Aldehydes - C H This group is always found on the end (terminal) carbon, carbon #1. In naming, again locate the longest chain that contains the functional group, number the aldehyde carbon as carbon #1, and replace the -e ending of the hydrocarbon with -al. Also, one and two carbon aldehydes have "common names", or names in addition to their IUPAC name that may be used. H C H methanal (formaldehyde) C C H ethanal(acetaldehyde) C. Ketones - C - The same double bonded oxygen as in the aldehyde, only it is on an internal carbon (any carbon except the first or last). Thus, the simplest ketone must consist of a three carbon chain. In naming, locate the longest chain containing the ketone group, number the carbons so the ketone carbon has the lowest possible number, and replace the -e ending of the hydrocarbon with -one. C C C C C C C propanone butanone (is 2 butanone necessary?) ************************************************************ The - C = part of any functional group is called a carbonyl group. The C H acid group also has its own name. It is called a carboxyl group. ************************************************************ D. Carboxylic Acids - C H
As in aldehydes, the acid group is always located on a terminal carbon. In naming, locate the longest chain that includes the acid group, number the acid group carbon as carbon #1 and replace the -e ending of the hydrocarbon with -oic acid. As with aldehydes, one and two carbon acids have common names. H C H methanoic acid (formic acid) C C H ethanoic acid (acetic acid) E. Ethers Ethers are somewhat different. An ether consists of an oxygen single bonded on each side by an alkyl group, as in C C. In naming ethers, name each alkyl group in alphabetical order and end with "ether". If the two alkyl groups are identical the prefix "di" is used. F. Esters C C C C C dimethyl ether ethylmethyl ether Esters are derived from carboxylic acids. A carboxylic acid contains the -CH group, and in an ester the hydrogen in this group is replaced by a hydrocarbon group of some kind. This could be an alkyl group like methyl or ethyl, or one containing a benzene ring. An ester name has two parts - the part that comes from the acid (ex. propanoic acid = propanoate) and the part that shows the alkyl group (ex. methyl making methyl propanoate ). Notice that the acid is named by counting up the total number of carbon atoms in the chain - including the one in the -CH group. So, for example, CH3CH2CH is propanoic acid, and the methyl group attached where the H was is named before the parent chain. C C C CH 3 methyl propanoate F. Amines - NH 2 These compounds contain a nitrogen with two hydrogens attached. In naming, locate the longest chain containing the amine group, and replace the -ane ending of the hydrocarbon with -amine. C NH 2 methamine