CHEM IUPAC naming~~急~~~20點

left: methylpropane or 2-methylpropane

Step 1: Confirm that it is a saturated hydrocarbon, without any function group or C=C or CΞC bond.

Step 2: Select the parent chain (i.e. longest hydrocarbon chain). It has 3 C atoms. Therefore, the parent name is propane.
AAC-C
AACC|
AAC-C-CA ← parent chain

Step 3: Assign the smallest number (2) to the branched chain (methyl group). The numbering of the parent chain is shown below.
AAC5-C
AAC5C|
AAC1-C2-C3A ← parent chain

Step 4: Put the name and number of the branched chain (i.e. 2-methyl) in front of the parent name (i.e. propane). Therefore, the IUPAC name of the left compound may be: 2-methylpropane.
However, according to the IUPAC rule, the number 2 may be omitted because there is no ambiguity (1-methylpropane and 3-methylpropane are impossible). Therefore, another IUPAC name (a better one) is: methylpropane.

==========
right: 4-methylpent-2-ene

Step 1: Confirm that it is an alkene with one C=C double bond, and without any function group.

Step 2: Select the parent chain (i.e. longest hydrocarbon chain with the C=C double bond). It has 5 C atoms. Therefore, the parent chain has 5 C atoms and 1 C=C double bond. Therefore, the parent name is pent-?-ene.
AAC-C
AACC|
AAC-C-C=C-CA ← parent chain

Step 3: Assign the smallest number to the C=C double bond, i.e. 2. Therefore, the parent name is pent-2-ene. The numbering of the parent chain is shown below.
AAC5-C
AAC5C|
AAC5-C4-C3=C2-C1A ← parent chain

Step 4: Put the name and number of the branched chain (i.e. 4-methyl) in front of the parent name (i.e. pent-2-ene). Therefore, the IUPAC name of the right compound may be: 4-methylpent-2-ene.

left: 2-methylpropane
right: 4-methylpent-2-ene

右邊的不是4methylpent-2-ene嗎？

2-METHYLPROPANE---LEFT
4METHYLPROPAN-2ENE--RIGHT.

....C.....
C - C-C
1...2...3

.. C..........
C-C-C=C-C
5. 4. 3. 2. 1