Answer
a. cis-1-bromo-1-propene
b. trans-4-ethyl-3-methyl-3-heptene
c. 1,4-diiodo-2-propyl-1-pentene
Work Step by Step
a. First, count the C atoms in straight chain. Here, it is 3. So, root name is 'prop' and ending name is 'ene' for double bond present. Now, numbering the C atoms in straight chain from right side so that substituent Br will at C1 position and also the double bond is between C1 and C2 carbon. So, '1-bromo' is added before root name and 1 is added before 'propene' to locate the position of the double bond.
Now, we see that two H atoms of two double bonded C atoms are on the same side i.e. cis to each other. So, this is a cis isomer.
So the complete name : cis-1-bromo-1-propene
b. no. of C atoms in longest straight chain = 7. so, root name is 'hept'. Numbering the C atoms in straight chain from left we found that the double bond is in between C3 and C4 position. ending name is 'ene' for double bond and 3 is added before hept to denote the position of the double bond i.e. 3-heptene. Now, look for the substituents present. Here, one methyl group is present at C3 position and one ethyl group is present at C4 position i.e. 4-ethyl-3-methyl is added before 3-heptene.
Now, we see that two ethyl groups attached with two double bonded C atoms are on the opposite side i.e. trans to each other. Hence, this is trans isomer.
complete name: trans-4-ethyl-3-methyl-3-heptene.
c. no. of C atoms in longest straight chain = 5. so, root name is 'pent'. Numbering the C atoms in straight chain from right to left we found that the double bond is in between C1 and C2 position. ending name is 'ene' and 1 is added before pent i.e. 1-pentene. Now, look for the substituents present. Here, two iodo groups are at C1 and C4 position respectively and one propyl group is at C2 position. i.e. 1,4-diiodo-2-propyl is added before 1-pentene.
Here, we see that four different groups are added to two double bonded C atoms so, no cis or trans isomer is possible here.
So, the complete name : 1,4-diiodo-2-propyl-1-pentene
