Organic Nomenclature Name Methane Butane Acetone Toluene Acetylene Ethyl Alcohol Formula CH4 C4H10 CH3COCH3 CH3C6H5 C2H2 C2H5OH First it should indicate how the carbon atoms of a given compound are bonded together in a characteristic lattice of chains and rings Second it should identify and locate any functional groups present in the compound Since hydrogen is such a common component of organic compounds its amount and locations can be assumed from the tetravalency of carbon and need not be specified in most cases The IUPAC nomenclature system is a set of logical rules devised and used by organic chemists to circumvent problems caused by arbitrary nomenclature Knowing these rules and given a structural formula one should be able to write a unique name for every distinct compound Likewise given a IUPAC name one should be able to write a structural formula In general an IUPAC name will have three essential features A root or base indicating a major chain or ring of carbon atoms found in the molecular structure A suffix or other element s designating functional groups that may be present in the compound Names of substituent groups other than hydrogen that complete the molecular structure As an introduction to the IUPAC nomenclature system we shall first consider compounds that have no specific functional groups Such compounds are composed only of carbon and hydrogen atoms bonded together by sigma bonds all carbons are sp3 hybridized Alkanes Hydrocarbons having no double or triple bond functional groups are classified as alkanes or cycloalkanes these hydrocarbons have no functional groups they constitute the framework on which functional groups are located in other classes of compounds provide an ideal starting point for studying and naming organic compounds The alkanes and cycloalkanes are also members of a larger class of compounds referred to as aliphatic aliphatic compounds are compounds that do not incorporate any a romatic ring molecular structure s in their Examples of Simple Unbranched Alkanes Name methane ethane propane butane pentane Molecular Formula Structural Formula Isomers Name Molecular Formula Structural Formula Isomers CH4 C2H6 C3H8 C4H10 C5H12 CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3 CH3 CH2 3CH3 1 1 1 2 3 hexane heptane octane nonane C6H14 C7H16 C8H18 C9H20 CH3 CH2 4CH3 CH3 CH2 5CH3 CH3 CH2 6CH3 CH3 CH2 7CH3 5 9 18 35 decane C10H22 CH3 CH2 8CH3 75 The IUPAC system SAYS we have names for simple unbranched chains we have names for simple alkyl groups that may be attached to the chains Examples of some common alkyl groups are given below the ane suffix is replaced by yl in naming groups l R is used to designate a generic unspecified alkyl group Group CH3 C2H5 CH3CH2CH2 CH3 2CH CH3CH2CH2CH2 CH3 2CHCH2 CH3CH2CH CH3 CH3 3C R Name Methyl Ethyl Propyl Isopropyl Butyl Isobutyl sec Butyl tert Butyl Alkyl IUPAC Rules for Alkane Nomenclature Find and name the longest continuous carbon chain Identify and name groups attached to this chain Number the chain consecutively starting at the end nearest a substituent group Designate the location of each substituent group by an appropriate number and name Assemble the name listing groups in alphabetical order using the full name e g cyclopropyl before isobutyl The prefixes di tri tetra etc used to designate several groups of the same kind are not considered when alphabetizing Cycloalkanes the general formula for a cycloalkane composed of n carbons is CnH2n Cycloalkanes have one or more rings of carbon atoms Although a cycloalkane has two fewer hydrogens than the equivalent alkane each carbon is bonded to four other atoms so such compounds are still considered to be saturated with hydrogen Examples of Simple Cycloalkanes Name Cyclopropan e Cyclobutan e Cyclopenta ne Cyclohexa ne Cyclohepta ne Cycloalkan e C3H6 C4H8 C5H10 C6H12 C7H14 CnH2n CH2 n Molecular Formula Structural Formula Line Formula Substituted cycloalkanes are named in a fashion very similar to that used for naming branched alkanes The chief difference in the rules the numbering starts at a substituted ring atom IUPAC Rules for Cycloalkane Nomenclature For a monosubstituted cycloalkane the ring supplies the root name table above and the substituent group is named as usual If the alkyl substituent is large and or complex the ring may be named as a substituent group on an alkane If two different substituents are present on the ring they are listed in alphabetical order and the first cited substituent is assigned to carbon 1 The numbering of ring carbons then continues in a direction clockwise or counter clockwise that affords the second substituent the lower possible location number If several substituents are present on the ring they are listed in alphabetical order Location numbers are assigned to the substituents so that one of them is at carbon 1 and the other locations have the lowest possible numbers counting in either a clockwise or counter clockwise direction The name is assembled listing groups in alphabetical order and giving each group if there are two or more a location number The prefixes di tri tetra etc used to designate several groups of the same kind are not considered when alphabetizing