Nomenclature of Organic Compounds PDF

NOMENCLATURE OF THE ORGANIC COMPOUNDS In order to give compounds a name, certain rules must be followed. When naming organic compounds, the IUPAC (International Union of Pure and Applied Chemistry) nomenclature (naming scheme) is used. This is to give consistency to the names. A good general rule...

NOMENCLATURE OF THE ORGANIC COMPOUNDS In order to give compounds a name, certain rules must be followed. When naming organic compounds, the IUPAC (International Union of Pure and Applied Chemistry) nomenclature (naming scheme) is used. This is to give consistency to the names. A good general rule to follow is to start at the end (the suffix) and work backwards (from right to left) in the name. STEP 1​ Recognise the functional group in the compound. This will determine the suffix of the name (a functional group is a specific set of atoms responsible for the characteristic chemical reactions of the molecule). Functional group suffix alkane -ane alkene -ene alcohol -ol (before you put the name of the alkane it comes from, without the E) STEP 2​ Find the longest continuous carbon chain that contains the functional group (it won't always be a straight chain) and count the number of carbon atoms in this chain. This number will determine the prefix (the beginning) of the compound's name.  ​ In this example, the longest continuous carbon chain is the one on the left. ​ ​ STEP 3 ​ Number the carbons in the longest carbon chain (Important: If the molecule is not an alkane (i.e. has a functional group like ALKENE OR ALCOHOL) you need to start numbering so that the functional group is on the carbon with the lowest possible number). Start with the carbon at the end closest to the functional group and ADD the number before the suffix -ene or -ol.  ​ Oct - 2 - ene In this example the Carbon number 1 is the one on the right (the one closer to the double bond). ​ Important: if there are branched groups, starts counting from the Carbon that is closer to the branched group. If more than one branched group are in the same position, start counting from the carbon closer to the branched group that comes first alphabetically (we will see this better later on). (1. Butyl, 2.Ethyl, 3. Isopropyl, 4. Methyl, 5. Propyl). ​ Important: the functional group (if present) has ALWAYS the priority over the branched group. STEP 4​ Look for any branched groups (or substituents). If there are no branched groups this step can be ignored. A branched group (also called ALKYL GROUP) is a part of a molecule that contains a branching point, where a carbon atom is attached to more than two other atoms or groups, forming a non-linear structure.​ ​  In this example the branched group is the CH3 attached to the third carbon of the longest carbon chain. Once you’ve located the branched group(s): ​ Name them by counting the number of carbon atoms in the branched group. Use the usual prefixes, and ADD -yl Methyl Ethyl  ​ Propyl ​ Important: if the branched group is a PROPYL, it can have 2 configurations: the linear one or the iso-conformation. You should give it the correct name. ​ Propyl on the left, isopropyl on the right ​ Isopropyl ​ Important: BUTYL has 3 different configurations, but we will not discuss them on this course. We will just use the main one. ​ Butyl ​ Note the position of the group on the main carbon chain (you represent the position with the NUMBER of the longest carbon chain that it is attached to it). ​ Write the position (number) and the name of the alkyl group BEFORE the name of the main chain in alphabetical order (ignoring di/tri/tetra if you have more than one alkyl group) 2-methylpropane ​ If there is more than one of the same type of branched group then all numbers must be listed and one of the prefixes listed in this table must be used (How many of the same type of branched group do you have?). Number of branched group of the Prefix same type 2 di- 3 tri- 4 tetra- ​ 2,3-dimethylbutane  ​ 2,2,4-trimethylhexane ​ Important: If the molecule is an alkane the branched group must be on the carbon with the lowest possible number.  STEP 5/a​ If the molecule is an ALKENE, you need to put the number of the carbon where the double bond begins before the final suffix (-ENE). ​ But-2-ene ​ But -1-ene ​ If there is more than one double bonds, before the suffix - ENE the final suffix changes in this: Number of double bonds in the Final suffix molecule 2 diene 3 triene 4 tetraene  Hex 1,4 ene STEP 5/b​ If the molecule is an ALCOHOL, you need to put the number of the carbon where the double bond begins before the final suffix (-OL). ​ Propan - 2 - ol ​ If there is more than one hydroxy group, before the suffix - ENE the final suffix changes in this: Number of hydroxy group Final suffix 2 diol 3 triol 4 tetraol  Butan-1,2-diol STEP 5/c​ If the ALKANE is a cyclic molecule, you just add the prefix CYCLO- before the root name of the molecule (the one referring to the number of carbons of the longest “carbon chain” (in this case “carbon ring”). ​ For a monosubstituted (only 1 branched group) cycloalkane, the ring supplies the root name and the substituent group is named as usual. A location number is unnecessary. ​ If you have more than 1 branched group, give the “number 1” to the carbon that has the branched group with the name that comes first alphabetically (The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing). The numbering of ring carbons then continues in a direction (clockwise or counter-clockwise) that affords the second substituent the lower possible location number.  Methylcyclohexane ​ 1 - Ethyl -3- methyl - 5 - propyl cycloheptane 1- Ethyl - 2 - methyl - 1 - propylcyclopentane SPECIAL CASES 1.​AROMATIC COMPOUNDS (ARENES) What Are Arenes? ​ Arenes are hydrocarbons with one or more benzene rings in their structure. ​ Benzene (C₆H₆) is the simplest arene, consisting of a hexagonal ring of six carbon atoms with alternating double bonds. Benzene ​ When the benzene ring is the main structure, it's named as "benzene." ​ Example: C₆H₆ is simply called "benzene." Substituents on Benzene: ​ If there are some substituents (branched groups) follow the same rules as for the cycloalkanes (add the name of the substituent as a prefix to "benzene.") 1,2 dimethyl benzene ​ If an Hydroxyl group (-OH) is attached to a benzene ring, it becomes a PHENOL Phenol