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The spread of organic chemistry resulted in a plethora of organic compounds with essentially the same condensed structural formula. The International Union for Pure and Applied Chemistry established a set of rules to ensure that the nomenclature of such compounds was homogenised and did not conflict with one another. The alkanes and cycloalkanes are also members of the aliphatic class of compounds. Simply put, aliphatic compounds are those that lack aromatic rings in their molecular structure
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Key Takeaways: Alkanes, Alkynes, Alkenes, Nomenclature, IUPAC nomenclature, Carbon
Read More: Carbon Tetrachloride
What is IUPAC Nomenclature?
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The International Union of Pure and Applied Chemistry's (IUPAC) nomenclature of organic chemistry is an approach of naming organic chemical compounds recommended by the International Union of Pure and Applied Chemistry (IUPAC). Inorganic chemistry has its own IUPAC nomenclature. Every organic compound has its own structural formula. The International Union of Pure and Applied Chemistry (IUPAC) is an acronym for the International Union of Pure and Applied Chemistry. It is a globally recognised international chemistry standards organisation that has named all chemical organic substances in a systematic manner. This naming convention for chemical organic substances is known as IUPAC nomenclature.
Alkanes
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Hydrocarbons with no double or triple bond functional groups are classified as alkanes or cycloalkanes, depending on whether the molecule's carbon atoms are arranged only in chains or also in rings. Although these hydrocarbons lack functional groups, they serve as the framework upon which functional groups in other classes of compounds are located, and they serve as an excellent starting point for studying and naming organic compounds.
The IUPAC names for simple continuous-chain alkanes from C-1 to C-10 are listed in the table below. These compounds are identified as alkanes by a common "ane" suffix. Longer chain alkanes are well known, with their names appearing in numerous reference and text books. Because they are the roots of many IUPAC names, the names methane through decane should be memorised. In naming carbon chains of five or more atoms, common numerical prefixes are used.
| Alkane | R–CH2–CH2–R | CnH2n+2 | The maximum H/C ratio for a given number of carbon atoms. |
IUPAC Nomenclature of Alkanes
- Locate and identify the longest continuous carbon chain.
- Identify and name the groups that are linked to this chain.
- Begin numbering the chain from the end closest to a substituent group and work your way down.
- It uses an appropriate number and name to each substituent group's location.
- Put the name together by listing groups alphabetically using the full name (e.g. cyclopropyl before isobutyl).
- When alphabetizing, the prefixes di, tri, tetra, and so on, which are used to designate several groups of the same kind, are not taken into account.
Read More: Condensation Polymerization
Alkenes and Alkynes
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Alkenes and alkynes are hydrocarbons with carbon-carbon double bond and carbon-carbon triple bond functional groups, respectively. The multiple bonding of the functional groups is reflected in the molecular formulas of these unsaturated hydrocarbons:
| Alkene | R–CH=CH–R | CnH2n | The number of hydrogen atoms is reduced by 2 in each double bond. |
| Alkyne | R–C≡C–R | CnH2n-2 | The number of hydrogen atoms is reduced by 4 in each triple bond. |
IUPAC Nomenclature of Alkenes
- An alkene or cycloalkene is indicated by the suffix (ending) ene.
- For the root name, the longest chain must include both carbon atoms of the double bond.
- The root chain must be numbered beginning at the end closest to a double bond carbon atom. If the double bond is in the chain's centre, the nearest substituent rule is used to determine where the numbering begins.
- If the compound contains more than one double bond, it is named with a diene, triene, or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.
IUPAC Nomenclature of Alkyne
- An alkyne or cycloalkyne is indicated by the yne suffix (ending).
- For the root name, the longest chain must include both carbon atoms of the triple bond.
- The root chain must be numbered beginning at the end closest to a triple bond carbon atom. If the triple bond is in the chain's centre, the nearest substituent rule is used to determine where the numbering begins.
- The triple bond locator is the smaller of the two numbers designating the carbon atoms of the triple bond.
- If there are multiple bonds, each must be assigned a locator number. In the IUPAC name, double bonds come before triple bonds, but the chain is numbered from the end closest to a multiple bond, regardless of its nature.
- Due to the linear nature of the triple bond, it can only be accommodated in rings with more than ten carbons.
- Substituent groups containing triple bonds are:
HC≡C– Ethynyl group
HC≡C–CH2– Propargyl group
Note:
| Unsaturated Carbon Chains - Alkene Formula Alkenes, which have the general formula CnH2n, are unsaturated hydrocarbons. It is the structure of a double bond compound. It has two fewer hydrogen atoms in the molecule than there are in an alkane with the same number of carbon atoms. |
Points to Remember
Following are some important points:
- Alkenes are hydrocarbons with two or more double bonds, whereas alkynes have one or more triple bonds. These compounds' naming conventions are similar to those of alkanes.
- The International Union of Pure and Applied Chemistry (IUPAC) updated their naming recommendation in 1993 to place the location number of the double bond before the -ene suffix of alkene names.
- Alkanes have the general formula of CnH2n+2 where n is the number of carbon atoms. Alkenes have the general formula CnH2n.
- The general formula for alkynes is CnH2n-2. The formula of Acetylene is C2H2.
- Alkenes are less stable than alkanes but more stable than alkynes; alkynes are more reactive than alkanes and alkenes.
Read More: Difference between Addition and Condensation Polymerization
Sample Questions
Ques: Define alkynes. (2 Marks)
Ans: Alkynes are organic compounds that have at least one triple bond in their structure or at the end of their chain. Their hydrogen atom count is twice the carbon constituent multiplied by two. The hydrogen atoms on the compound are easily detached by a metal base material (electrophile). As a result, understanding the various alkynes' reactions aids in the prevention of corrosion, which can occur when alkynes come into contact with metal.
Ques: Describe the Formula and structure of Alkanes. (2 Marks)
Ans: CnH2n+2 is the general formula for alkanes.
Here, n denotes the number of carbon atoms in their chemical structure. As a result, the number of hydrogen atoms is 2n+2. This chemical formula applies to all saturated hydrocarbons.
Methane (CH4) is the most basic alkane. With single bonds, one carbon atom is bonded to four hydrogen atoms. As a result, carbon's four valence electrons will bond with the one valence electron of each hydrogen atom. As a result, a completely saturated hydrocarbon is formed.
Ques: Describe the physical properties of Alkenes. (2 Marks)
Ans: The physical properties of alkenes:
- The regularity of the packing, or the closeness of these molecules, determines the melting and boiling points of alkenes.
- Alkene isomers with higher melting and boiling points but weaker dispersion forces have higher melting and boiling points than molecules with the same molecular formula but weaker dispersion forces.
- Non-polar alkenes are not immiscible in water and have a lower density than water.
- They are soluble in organic solvents. Furthermore, they do not conduct electricity.
Ques: Give a definition for Alkanes. (2 Marks)
Ans: Alkanes are chemical compounds made up of carbon (C) and hydrogen (H) atoms; thus, they are also known as hydrocarbons. Alkanes have only one bond in their chemical structure. This diagram depicts the chemical structures of two alkanes: ethane and pentane. Looking at ethane and pentane, these alkanes are referred to as saturated because they only contain single bonds, resulting in each carbon atom being saturated with hydrogen atoms. As a result, alkanes are classified as saturated hydrocarbons.
Ques: Describe the Properties of Alkynes. (2 Marks)
Ans: The properties of alkynes follow a similar pattern to those of alkanes and alkenes.
- Alkynes are unsaturated carbons with three bonds at the carbon site.
- Except for ethylene, which has a slight distinctive odour, all alkynes are odourless and colourless.
- The first three alkynes are gases, followed by eight liquids. All alkynes above these eleven are solids.
- Alkynes have a slightly polar nature.
Ques: Give a definition for IUPAC. (2 Marks)
Ans: IUPAC (International Union for Pure and Applied Chemistry) established a common naming system based on standard rules. IUPAC nomenclature is the name given to this method of naming. There are several nomenclatures in chemistry: in addition to elements and compounds, reactions methods, pieces of apparatus, and theoretical concepts are all named, resulting in a very organised and systematic process.
Ques: Define Polymerization. (2 Marks)
Ans: Polymerization is any chemical process in which relatively small molecules, known as monomers, combine to form a very large chainlike or network molecule known as a polymer.
Ques: Give a definition for Alkenes. (2 Marks)
Ans: Alkenes are unsaturated hydrocarbons with a double bond between the carbon atoms. CnH2n is the generic formula for alkenes. The terms alkenes and olefin are frequently used interchangeably. Olefin is derived from the Greek phrase olefin gas, which means oil-forming gas. Because of the presence of double bonds, alkenes are extremely reactive chemically.
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