Organic Chemistry -the study of carbon compounds -there are millions of carbon compounds while there are less than 50,000 compounds of all other elements combined -primary sources of carbon compounds include petroleum (oil), plants and animals Life is Organic Chemistry Properties of Organic Compounds • Organic compounds have covalent bonding and thus have low melting points, generally less than 300˚C • Organic compounds are generally nonpolar and therefore insoluble in water, although low molecular mass alcohols, organic acids and amines are water soluble • Organic compounds are generally nonelectrolytes (do not produce conductive solutions in water) • Organic acids such as ethanoic acid(acetic acid) are electrolytes • Carbon has four valence electrons (2s2, 2p2) • Carbon needs to form four covalent bonds in order to complete the valence shell • Carbon undergoes sp3 hybridization to form four bonds • The four bonds of carbon are directed toward the corners of a tetrahedron • Carbon atoms can form single double or triple bonds by sharing one, two or three pairs of electrons • Carbon atoms can bond to each other to form long chains, branched or cyclic compounds . C: . . .C. . Hydrocarbons • Include only carbon and hydrogen atoms • Include the homologous series – Alkanes have only single bonds between carbons – Alkenes have a carbon-carbon double bond – Alkynes have a carbon-carbon triple bond Alkanes • Are saturated molecules, meaning they have all single bonds and cannot add any more atoms • Are also called the paraffin series • Names end in -ane • Have the general formula CnH(2n+2) • The simplest is CH4 which is the main component of natural gas • Are used as fuels in combustion reactions • Can undergo substitution reactions with halogens Naming Organic Compounds • count the number of carbons in the longest C to C chain • Select the appropriate prefix from Table P • Look for double or triple bonds in the carbon chain – All single bonds, name ends in –ane – Double bond present, name ends in –ene – triple bond present, name ends in -yne Prefixes for carbon chains (Table P of reference tables) • • • • • • • • • • • # of C’s 1 2 3 4 5 6 7 8 9 10 Prefix methethpropbutpenthexheptoctnondec- When the carbon group is a side chain off of the main chain, it is named by adding -yl to the prefix and describing it’s location by carbon number Start the numbering at the end of the chain that will give the lowest number for the address of the side chain 3-ethyl octane Isomers • Isomers are compounds which have the same molecular formula, but different structural formulas (arrangement of atoms) • In the alkanes, isomers are possible beginning with four carbons; The first three carbons are linked end to end, but the fourth carbon may be added to the end of the chain or added to the side at the middle carbon • The more carbon atoms, the more possible isomeric structures Butane C4H10 2-methyl propane C4H10 Alkenes • Contain a carbon-carbon double bond • Have the general formula CnH(2n) • Are unsaturated and can undergo addition reactions • Names end in –ene • Describe location of double bond with carbon number where it starts • Number the chain to give the multiple bond the lowest possible number H2C CH2 ethene CH2 CH3 propene Alkenes • Ethene and propene do not need numbering for the double bond because the position is unambiguous • 1-butene and 2-butene are isomers • Isomers have the same molecular formula, but different structural formulas CH3 H2C 1-butene H3C 2-butene CH3 Alkynes • Contain a triple carbon-carbon bond • Have general formula CnH(2n-2) • Names end in –yne • Also called the acetylene series after the first member • Are unsaturated and can undergo addition HC Acetylene CH C2H2 IUPAC name is ethyne Functional groups Table R of the reference tables • Functional groups contain atoms other than C and H • The most common functional groups include halogens, and groups containing oxygen and nitrogen atoms • There are different suffixes to compound names to describe most of the functional groups Functional groups • Functional groups are atoms other than carbon and hydrogen in the carbon and chain • Halogen: fluoro-, chloro-, bromo-, and iodo- are described by their position • For multiple substitution, prefixes are used • 2= di3 = tri- 4 = tetr(a) 5 = pent(a) • For five and above the prefixes are the same as the ones used in table P for the carbon chain numbers • Each substituent gets a number, so there must be three numbers for tri-, 5 for penta, etc H Cl H Cl H H H H 1,2-dichloropropane H H Br Br H Br H Br 1,1,3,3-tetrabromopropane Alcohols • Contain oxygen atoms • Alcohols have an –OH group on the carbon chain • Alcohol names end in the suffix –ol, just like the word alcohol • The simplest alcohols are methanol and ethanol with just one or two carbons, respectively methanol CH3OH ethanol C2H5OH Primary, Secondary and Tertiary Alcohols 1-propanol Primary alcohol • 1-propanol is a primary alcohol with the –OH group on an end carbon attached to only one other carbon 2-propanol • 2-propanol is a secondary alcohol with the –OH carbon attached to two other carbons Secondary alcohol • 2-methyl-2-propanol is tertiary alcohol because the alcohol carbon is attached to three other carbons 2-methyl-2-propanol Tertiary alcohol Ethers • Ethers are molecules with an oxygen atom between two alkyl groups: R-O-R • An ether can be prepared by dehydration (aka condensation) of two primary alcohols • Ethers are named by using the prefixes for each alkyl group followed by the word ether • CH3OH + C2H5OHCH3OC2H5 + H20 • Methanol + ethanol ethyl methyl ether • The order of the alkyl groups is alphabetical Ethers • Unlike alcohols, ethers cannot hydrogen bond between molecules so their boiling points are lower than alcohols of similar mass, and their vapor pressures are higher • Diethyl ether was used as an anesthetic, but its volatility and flammability made it very hazardous to use, and less volatile/flammable anesthetics were developed Amines • Amines contain a nitrogen heteroatom • Low molecular mass amines have high vapor pressures and offensive odors • The putrid odors of decomposing fish or meat are caused by organic amines • Amines can be primary, secondary or tertiary, depending on whether 1, 2 or 3 alkyl groups have replaced the hydrogens on ammonia, NH3 • CH3NH2 is a primary amine • (CH3)2NH is a secondary amine • (CH3) 3N is a tertiary amine