Organic Chemistry study deals with the production of organic molecules and their reaction paths, interactions, and uses. Organic chemistry is a branch of chemistry that deals with the study of the structures, composition, and synthesis of carbon-containing compounds. For a good understanding of this type of chemistry, it is essential to make a note of the fact that that every organic molecule in addition to containing carbon also contains hydrogen. Although it is true that organic compounds can contain other elements, it is the bond between carbon and hydrogen that makes a compound organic.
Initially, Organic Chemistry was defined as the study of compounds formed by living organisms, but the definition was later widened to also encompass synthetically synthesized substances. Prior to the year 1828, every organic compound was obtained from living organisms.
Nomenclature of Alkanes
The table below illustrates the systematic names and arrangements of the first twenty straight chain alkanes. It is essential to get familiar with them as form the basis for naming countless other organic molecules all through your course of study.
Alkanes can be depicted by the general formula CnH2n+2. An alkyl group is derived by removing one hydrogen from the alkane chain, and it can be depicted by the formula CnH2n+1. The removal of the one hydrogen gave rise to a stem change from -ane to –yl as exemplified in the examples below:
Similar concept can be applied to every straight chain alkane available in the table below:
Name Molecular Formula Condensed Structural Formula
Methane – CH4 – CH4
Ethane – C2H6 – CH3CH3
Propane – C3H8 – CH3CH2CH3
Butane – C4H10 – CH3(CH2)2CH3
Pentane – C5H12 – CH3(CH2)3CH3
Hexane – C6H14 – CH3(CH2)4CH3
Heptane – C7H16 – CH3(CH2)5CH3
Octane – C8H18 – CH3(CH2)6CH3
Nonane – C9H20 – CH3(CH2)7CH3
Decane – C10H22 – CH3(CH2)8CH3
Undecane – C11H24 – CH3(CH2)9CH3
Dodecane – C12H26 – CH3(CH2)10CH3
Tridecane – C13H28 – CH3(CH2)11CH3
Tetradecane – C14H30 – CH3(CH2)12CH3
Pentadecane – C15H32 – CH3(CH2)13CH3
Hexadecane – C16H34 – CH3(CH2)14CH3
Heptadecane – C17H36 – CH3(CH2)15CH3
Octadecane – C18H38 – CH3(CH2)16CH3
Nonadecane – C19H40 – CH3(CH2)17CH3
Eicosane – C20H42 – CH3(CH2)18CH3
Alkoxides are composed of an organic group bonded an oxygen atom that is negatively charged. Generally, they are written as RO-, where R stands for the organic substituent. Related to what obtainable in alkyl groups earlier discussed, the concept of naming alkoxides can be applied to every straight chain alkanes in the above table. and so on.
Three Basic Principles of Naming in organic chemistry
Select the longest, mainly substituted carbon chain containing a functional group.
A carbon that is bonded to a functional group must be the carbon atom in the chain with the lowest possible number. If there are no functional groups, next any substitute present should be given the smallest possible number.
After putting the 1st and second rules into consideration, ensure that you consider the alphabetical order and that your substitutes and/or functional groups are noted in alphabetical order.
Common Names of Branched Alkanes
A number of branched alkanes have common names that are still widely made use of today. These common names use prefixes like iso-, sec-, tert-, and neo-. The prefix iso-, stands for isomer. It is frequently given the name 2-methyl alkanes. What this means is that during naming, if there is methyl group situated on the second carbon of a carbon chain during naming, we could make use of the prefix iso-. The prefix will be placed in front of the alkane name which showcases the total number of carbons.
• Isopentane. This is the same as 2-methylbutane
• Isobutene This is the same as 2-methylpropane
To be able to allocate the prefixes sec-, which represents secondary, and tert-, which represents tertiary, it is essential that we first and foremost study how to classify carbon molecules. If a carbon is attached to only one other carbon, it is referred to as a primary carbon. If a carbon is attached to two other carbons, it is referred to a secondary carbon. A tertiary carbon is a carbon atom attached to three other carbons and finally, a quaternary carbon is a carbon that has carbon atom attached to it.
• 4-sec-butylheptane (30g)
• 4-tert-butyl-5-isopropylhexane (30d);
Example of the usage of the prefix neo-
Nomenclatures of Alkenes
Alkenes are a class of hydrocarbons that contain only carbon and hydrogen with a double bond. They are unsaturated compounds that contain at in the slightest one carbon-to-carbon double bond. Alkenes are also known as olefins.
Alkenes possesses carbon-carbon double bonds and are unsaturated hydrocarbons with the molecular formula is CnH2n. This is as well the same molecular formula that of cycloalkanes. Alkenes are named by leaving off the -ane ending of the parent alkane and replacing it with -ene.
Introduction of Alkene
The parent structure is the longest chain containing both carbon atoms of the double bond. The two carbon atoms of a double bond and the four atoms attached to them recline in a flat surface, with bond angles of approximately 120°. A double bond consists of one sigma bond created by overlap of sp2 hybrid orbitals and one pi bond fashioned by overlap of parallel 2 p orbitals.
The Basic Rules
For straight chain alkenes, it is equivalent basic rules as nomenclature of alkanes apart from the alteration with the suffix to “-ene.”
i. Discover the Longest Carbon Chain that is bearing the Carbon to Carbon double bond. In a situation where we have two ties for longest Carbon chain, and both chains is bearing a Carbon to Carbon double bond, the most substituted chain should be discovered.
ii. The Carbon to Carbon double bond should be given the lowest possible number.
There is no need to number cycloalkenes due to the fact that the double bond is situated one position.
Alkene that possess equivalent molecular formula but which has the double bonds located in a different position is referred to as constitutional isomers.
The priority of Functional Groups during naming:
iii. After the two rules above, add substituents and their location to the alkene as prefixes. Do keep in mind to assign the lowest possible numbers. You must not forget to name them in alphabetical order when writing them.
iv. The next thing to do is to identify stereoisomers. When there are only two non hydrogen that are attached to the alkene, you should use cis and trans to name the molecule.
v. On the contrary when there there are 3 or 4 non-hydrogen dissimilar atoms attached to the alkene , you should use the E, Z system.
vi. Note that the hydroxyl group proceeds over the double bond. Consequently, alkenes possessing alcohol groups are referred to as alkenols. And the prefix for this group becomes -enol. And this means that in this group, the alcohol takes up the lowest priority against the alkene.
vii. Finally, note that alkene substituents are called alkenyl with the suffix -enyl.
Below is the systematic name and molecular formula of the first twenty straight chain alkenes.
Name – Molecular formula
Ethene – C2H4
Propene – C3H6
Butene – C4H8
Pentene – C5H10
Hexene – C6H12
Heptene – C7H14
Octene – C8H16
Nonene – C9H18
Decene – C10H20
Undecene – C11H22
Dodecene – C12H24
Tridecene – C13H26
Tetradecene – C14H28
Pentadecene – C15H30
Hexadecene – C16H32
Heptadecene – C17H34
Octadecene – C18H36
Nonadecene – C19H38
Eicosene – C20H40
Double bonds can occur as geometric isomers and these isomers are selected by making use of the cis / trans designation or the modern E / Z designation.
For Cis Isomers, the two largest groups are on the same side of the double bond.
For trans Isomers, the two largest groups are on the opposite sides of the double bond.