Organic Chemistry
28th Apr 2021 @ 10 min read
What is Organic Chemistry?
Chemistry is the subject of different elements of the Mendeleev’s periodic table, reactions and mechanisms, physical and chemical properties and finally the application of these elements. There are 118 elements reported in nature and only one element, which is carbon [Atomic no 6, symbol C] is founder of organic chemistry discipline.
Organic chemistry is one of the branches of chemistry that deals with molecules, compounds and polymeric network originating from carbon element. It is popularly also known as chemistry of carbon.
Organic chemistry functional groups
When we study the carbon compounds, we classify or categorize them into many groups. This classification is based on the chemical structure and reactions, physical and chemical properties of the functional groups. A functional group is set of atoms bonded together and are shown in Table 1. To understand this, some carbon compounds are categorized as alkanes, alkenes, alkynes, alcohols, aldehydes, ketones, carboxylic acids and many other. To identify any category, we use a functional a group to designate a carbon compound.
Table 1: Functional groups
| Functional group name | Functional group identification | Functional group name end |
| Alkane | R-H, R-R | -ane |
| Alkene | R=R | -ene |
| Alkyne | R | -yne |
| Alcohol | R-OH | -ol |
| Aldehyde | R-CHO | -al |
| Ketone | R-CO-R | -one |
| Carboxylic acid | RCOOH | -oic |
| Amine | RNH2 | -amine |
| Ester | RCOOR’ | -ate |
| Amide | RCONH2 | -amide |
| Ether | ROR’ | -ether |
· R refers to alkyl group [A carbon bonded to hydrogens! Remember that each carbon can only form four bonds]
Organic chemistry reactions
The reactions carried out by carbon compounds can be classified as organic chemistry reactions. These reactions are of various types such as:
Reduction reaction : A reaction in which a hydrogen is added to carbon compound OR an oxygen is lost from the carbon compound.
Oxidation reaction: A reaction in which hydrogen is lost from the carbon compound OR the carbon compound gains an oxygen.
Substitution reaction: A reaction in which one functional group is replaced by the other functional group.
Addition reaction: A reaction where hydrogen or any other functional group is added to a carbon compound.
Elimination reaction: A reaction in which hydrogen or any other functional group is eliminated.
Compounds with carbon number 17
Carbon compounds connect and forms long chain compounds and forming polymers. The carbon compound with 17 carbon in its chemical structure and the simplest among the series is known as heptadecane. There are 24984 isomers of C-17 carbon compounds, in which carbon can bond with the hydrogen, oxygen, halogens, nitrogen, sulphur etc.
Nomenclature of carbon compounds containing functional groups
Nomenclature of carbon compound is giving a name to a carbon compound. As we have studied earlier during the identification of functional group, the naming is done according to IUPAC rules of nomenclature. However, sometime these compounds are popularly known by their common names. Before we understand the naming, we have to simply remember some points:
Tip ! Carbon series starts with a prime name in a carbon compound as shown below:
1. One carbon : Meth-
2. Two carbons : Eth-
3. Three carbons: Prop-
4. Four carbons: But-
5. Five carbons: Pent-
6. Six carbons: Hex-
7. Seven carbons: Hept-
8. Eight carbons: Oct-
9. Nine carbons: Non-
10. Ten carbons: Dec-
The naming of the carbon compound is done based on functional group attached to a carbon compound as provided in Table 2.
Table 2: Naming of functional groups
| Functional group name | Functional group identification | Functional group name end | Example [Based on the smallest member of the group] | Chemical structure | Other Examples |
| Alkane | R-H, R-R | -ane | Methane | CH4 | Ethane, propane, but ane |
| Alkene | R=R | -ene | Ethene | C2H6 | Propene, butene, pentene |
| Alkyne | R | -yne | Ethyne | C2H2 | Propyne, butyne, pent yne |
| Alcohol | R-OH | -ol | Methanol | CH3OH | Ethanol, propanol, butan ol |
| Aldehyde | R-CHO | -al | Methanal | HCHO | Ethanal, propanal, butan al |
| Ketone | R-CO-R | -one | Propanone | CH3COCH3 | Butanone, pentanone, hexanone |
| Carboxylic acid | HCOOH | -oic | Methanoic acid OR Common name Formic acid | HCOOH | Ethanoic acid, propanoic acid |
Note !!! When a hydrogen from a carbon compound is replaced by a functional group, then the name changes accordingly. The position where the hydrogen is replaced by a functional group will now become part of the name. Example
CH3CH2CH3: If hydrogen is replaced by bromine from either first carbon or third carbon then the structure would look like below:
CH2(Br)CH2CH3 / CH3CH 2CH2Br, the name would be 1-Bromopropane OR 1-Propyl bromide
[Tip! The position of the functional group prioritise the position of carbon, therefore we do not expect 3-Bromopropane, even though in a structure the bromo group is on third carbon]
If hydrogen is replaced by bromine from second carbon, then the structure would look like below:
CH3CHBrCH3, the name would be 2-Bromoprpane OR 2-Propylbromide
How to memorize organic chemistry reactions
To answer this, the reactions SHOULD NOT BE memorized, rather understand the reactions and what parameters [such as reactants, temperature, solvent, time, pH etc] play a huge role for a reaction. It is better to understand the concept and apply accordingly.
[Remember! There are many other factors such as electronegativity, resonance effect, hyperconjugation, mesomeric effect and many others that decide the nature of a carbon compound and it can differ in the same series. So the reaction that is possible for smaller member of a carbon series may not be successful for bigger member of the same series and vice versa]
What does the terms organic mean in chemistry?
Organic refers to carbon in chemistry
What is an R group in organic chemistry?
R group refers to an alkyl group. Some examples are given below:
1. CH4 is Methane where as CH3- is a methyl group
2. C2H6 is Ethane where as C2H5 - is an ethyl group
3. C3H8 is propane whereas C3H7 - is propyl group
[Note! When a hydrogen from a carbon compound is replaced, the carbon compound become an alkyl group]
Alkyl group is a general name indicating a group from alkane series with one less carbon
Example:
C5H10 is pentane
C5H9 OH is pentyl alcohol or pentanol
What does pH stand for in organic chemistry?
pH in any branch of chemistry is a scale that indicate the hydronium/hydrogen ion concentration in a liquid or a solvent making it either acidic [pH less than 7], neutral [pH=7] or basic[pH greater than7].
For examples : Hydrocarbons, Alcohols, Aldehydes, Esters, Amides, Ketones are neutral compounds with neutral pH. Carboxylic acids, Nucleic acids are acidic compounds with acidic pH. Amines and Nitrogen containing heterocyclic compounds are organic bases with basic pH.
What is conjugation in organic chemistry?
An organic compound or a carbon compound can have sigma bonds (single bonds due to s-orbitals) and /or pi-bonds due to p-orbital (double or triple bonds) in its molecular structure. Not to get confused that a carbon compound CAN NOT be made up of ONLY pi bonds but it also has sigma bonds. However, it CAN BE made up of ONLY sigma bonds.
If a compound contain pi-bonds, then conjugation play a role.
Conjugation is linking of these pi bonds together to provide extra stability to the molecule .
Conjugation occurs in a carbon compound with alternate single and multiple (double/triple) bonds.
No conjugation occurs if there are no alternate single and multiple bonds
What is reflux in organic chemistry
Reflux term is used for some experiments in organic chemistry where the concentration of some of the reactants should be constant throughout the reactions. In some experiments, reflux set up is used. The reactants are heated up and rises until it reaches condenser where these are condensed back to the reaction vessel. This process is termed as reflux in organic chemistry.
What are structural formulas used in organic chemistry?
There are different formulas to represent a carbon compound. Given below are the widely used structural formulas in organic chemistry:
1. Straight chain formula: This is a formula of a carbon compound in which all the atoms and
the bonds are distinctly seen as a straight chain.
2. Condensed formula: In this formula , different groups of the carbon compound are
condensed together.
3. Line bond OR line angle formula: This is the formula where structure is shown as a line
representing the two ends as a carbon and a line as a bond.
How to calculate equivalents in organic chemistry?
Equivalents in organic chemistry refers to the number of moles of a carbon compound reaction with number of moles of other reactant normally a limiting reagent (limiting reagent: a reagent that is completely used up in a reaction) to form products. To calculate equivalents the whole equation of a reaction should be written with correct stoichiometry.
For instance, consider a reaction between 6 mole of aniline (reactant) with 3 mole acetic anhydride (limiting reagent).
The molar equivalents of aniline would be:
How to draw resonance structures in organic chemistry?
Resonance is a phenomenon that occurs in those carbon molecules/ions that have lone pair of electrons and can be delocalized [flow freely from one atom to another] within the structure. To draw, one should know how to draw Lewis structure of the carbon compound and how the electron should move from one atom to another. Resonance indicate that there is no real structure but an overall resonance hybrid structure.
What is optical activity in organic chemistry
Optical activity by carbon compounds is their ability to rotate plane polarised light to either right or left hand side. The carbon compounds should be chiral (when a carbon atom is bonded to four different functional groups) in nature. The rotation of light is done by enantiomers (mirror images) of the chiral compounds.
The mirror images of a chiral carbon compound are also known as enantiomers, which can cause the optical activity.
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05th Jul 2021
