C4H8, an alkene can show geometrical isomerism, functional isomerism and structural isomerism. According to the structure, chemical and physical properties such as reactivity, reaction rate, melting and boiling point of C4H8 vary.
In this tutorial, we will learn how to draw isomers for chemical formula, C4H8.
Finally, we do a question for explaining how to identify a correct isomer by understanding characteristics of C4H8 isomers.
In isomerism, there are two types, structural and stereoisomerism. Isomers for C4H8 can be drawn for both types.
First two types of isomers belong to aliphatic organic compound types and third type is cyclic organic compounds.
Before start to draw isomers, we should identify the organic compound type. In C4H8, there are only carbon and hydrogen. So this compound is a hydrocarbon. After observing the molecular formula, we can decide C4H8 is an alkene because it follows the general formula of alkene, CnH2n.
First, simplest structure of C4H8 should be drawn and changes should be done to that drawn structure as giving new isomers. These changes are changing the structure of carbon chain or changing the position of double bond and more.
As the first isomer, draw all carbon atoms as a linear structure with a double bond between two carbon atoms. (in actual, all four carbon atoms are not in a linear line. For better understanding we say, carbon atoms should be in a same line). Put the double bond to the end of carbon chain and add hydrogen atoms to the carbon atoms. Study following structure.
Under structural isomerism, position and chain isomers can be drawn for C4H8.
The compounds which have same number molecular formula but differ in the position of the functional group, carbon-carbon multiple bond or substitute group are called position isomers and this kind of isomerism is defined as position isomerism.
C4H8 has two position isomers. Position isomers of C4H8 are drawn by changing the position of double bond.
We change the arrangement of carbon chain in the molecule. As the first step, there was only one carbon chain. Now, we brake that carbon chain to several parts.
When chain isomerism of C4H8 is drawn, you can see its IUPAC name is different from IUPAC names of position isomers. In the chain isomer, there is a root chain and a substituent chain.
In C4H8, we can draw two geometrical isomers as cis and trans.
In cis structure, -CH3 is placed in same side of the double bond. But in trans structure, -CH3 groups are placed at opposite sites.
Physical and chemical properties of cis and trans structures are different.
When each carbon joins with two -CH2 groups, a cyclic isomer can be drawn. When its chain is changed, another isomer can be obtained. See cyclic isomers of C4H8 in the following figure.
Cyclic isomers can show chain isomerism too due to different arrangement of carbon chain.
In cyclic isomer structures of C4H8, there are no double bonds between carbon atoms. Therefore, reactions of cyclic isomers should be different from other isomer structures.
A is a compound which has C4H8 molecular formula and it is not a cyclic compound . A has following properties.
Can you guess which isomers can show above characteristics?
In the last experiment, hydrogen gas is released. If hydrogen gas is released, C can be a an alcohol compound or a phenol compound or a carboxylic acid compound or an alkyne which contains acidic hydrogen. We can remove phenol from our answers set because phenol is an aromatic compound.
In first experiment, a bromine molecule is added to the C4H4 molecule and alkyl halide should be given as the product. Then, in the next step, given product is heated with alcoholic KOH. You know, when alkyl halide is heated with alcoholic KOH, alkene or alkyne can be given as the product according to the locations of bromine atoms (to give an alkyne, there sholud be at least two halogen atoms) .
But-1-en, But-2-en and 2-methylprop-1-en are examples of structural isomers of C4H8
There are two types of isomerism in stereoismers as optical and geometric. For C4H8 structure, we can only draw geometric isomerism and they are illustrated above in this tutorial. We cannot make a carbon atom which has four different groups to make a optical isomerism.
To have optical isomerism, four different groups should be connected to a carbon atom in the molecule. Let's try to do that for C4H8 molecule.
Due to formation of alkene group, at least two carbon atoms are required. So only two carbon atoms are remaining now to complete the rest of the molecule because C4H8 molecule has only four carbon atoms. We know, carbon atoms which are in the double bond cannot show optical isomerism because they cannot make different four bonds with four different groups.
Then, other two carbon atoms also cannot show optical isomerism because there is not enough different groups.
Yes. When carbon chain is changed like structural isomerism, IUPAC name is changed because total structure of molecule is different from previous one. As examples for C4H8 , butene, 2-methylpropene, and 2-butene are different IUPAC names for C4H8 isomers.
Five isomers can be drawn incloding cyclic isomers, cis and trans isomers.
Due to occurrence of more than three carbon atoms, chain isomers are possible. When number of carbon atom is more than three, one carbon atom can (in middle part of the molecule) can join with two carbon atoms or three carbon atoms. So it makes possible for chain isomers for C4H8 because it has four carbon atoms.
In functional isomers, functional group (alkene group in the C4H8) should be changed to another functional group. For C4H8, we cannot draw functional isomers.
But, for C4H6 molecule, we can draw functional isomers because it is an alkyne. Alkyne group can be represented as two alkene groups. So try to draw isomers of C4H6 molecule.
Though there are different isomers for C4H8, they react with dilute H2SO4 acid and hydrolysis to give alcohols.
But, alcohol type (primary, secondary and tertiary)is different according to the isomers of C4H8.
Two cyclic isomers are possible for C4H8.
In this tutorial, we have explained how to draw isomers properly.