Question

The general molecular formula for alkanes is CnH2n+2. What is the general molecular formula for cycloalkanes with two rings?

Answer 1

`\huge \boxed{{C_nH_(2n-2)}}`

Step-by-step explanation:

The formula for one ring cycloalkanes is:

`C_nH_(2n)`

Cycloalkanes with two rings have two less hydrogen atoms.

`C_nH_(2n-2)`

Answer 2

• The general molecular formula for cycloalkanes with two rings is:

`C_nH_(2n-2)`

Step-by-step explanation:

As stated in the question statement, the general formula for an alkane is:

`C_nH_(2n+2)`

That is because each of the two carbons of the ends are bonded to three hydrogen atoms and the other carbons are bonded to two atoms:

This example shows you how that works.

Assume a four carbon linear chain, i.e. n = 4:

• Two carbons of the ends ↔ six hydrogens
• Two internal carbons ↔ four hydrogens
• 2 + 2 = 4 carbons ↔ 6 + 4 = 10 hydrogens
• 4 ↔ 2×4 + 2

For an alkane of one ring or with one ring, the general formula is:

`C_nH_(2n)`

That is because there not ending carbons: every carbon atom is attached to other carbon atom and two hydrogen atoms.

If you add a second ring, the molecule will have two less hydrogen atoms relative to the alkance with one ring, because you are adding one extra carbon - carbon bond, reducing the number of hydrogen atoms attached in two.

Thus, the general formula for cycloalkanes with two rings is:

`C_nH_(2n-2)`