Question

What is the molecular formula for $3 -$ Ethyl $- 2,3$ $-$ dimethyl pentane?

Answer 1

Molecular formula gives the total number of atoms of each element in a molecule of the given substance. The molecular formula for the chemical formula is assigned according to the rules of the international union of pure and applied chemistry called IUPAC. The structures drawn for the given configuration will give the molecular formula.

Complete step by step answer:
The international union of pure and applied chemistry rules are stated as follows:
(a) Recognize the functional group in the compound. That will determine the suffix of the name.
(b) Then we will take the longest continuous chain length that contains the functional group and count the number of carbon atoms in the chain. The prefix is determined by the number
(c) Then we will number the carbon in the longest chain. The numbering should be so that the functional group is on the carbon with the lowest possible number. We will start with the carbon at the end closest to the functional group.
(d) Look for the only branched group:-
Do the naming by counting the number of carbon atoms in the branched group.
Write the position of the group on the main carbon chain. If there is more than one same type of branched group then both numbers must be listed. For example- (2,4−) and one of the prefixes must be used.
The branched group must be listed before the name of the main chain in alphabetical order

Number	Prefix
2	di-
3	Tri-
4	Tetra-

Now we have been given $3 -$ Ethyl $- 2,3$ $-$ dimethyl pentane

The molecular formula is as follows
$C{H_3} - CHC{H_3} - C(C{H_3}C{H_2}C{H_3}) - C{H_2} - C{H_3}$
Hence the molecular formula is ${C_9}{H_{20}}$

Note: The above molecular formula is in accordance with the rules assigned by the IUPAC. The molecular formula tells the total number of atoms present in a particular molecule. The molecular formula has been derived from that concept.