English Language and Literature homework help. You convert the molecular formula to its equivalent alkane formula. Then you compare the number of H atoms to those in the alkane with the number of C atoms.
The degree of unsaturation or U-value gives the total number of rings and double bonds in a molecule. Here’s a way to calculate it.
The formula for an alkane is ##C_nH_(2n+2)##. Hexane is C?H??.
The formulas for hexene and cyclohexane are C?H??. Thus, the introduction of a double bond or a ring removes 2 H atoms. Each ring or double bond counts as a degree of unsaturation. A triple bond counts as two double bonds.
We could write this as
U = ½(H atoms in alkane H atoms in compound).
If we have a compound with formula C?H?, the saturated alkane would be C?H?. Then U = ½(8 4) = 2.
This tells that the molecule must have 2 double bonds, 1 ring + 1 double bond, 2 rings, or a triple bond. It must be either propa-1,2-diene, cyclopropene, or propyne.
If there are heteroatoms X, we make the following substitutions:
Group 17: X ? H
Group 16: Ignore
Group 15: X ? CH
Group 14: X ? C
Thus,
C?H?N ? C?H?(CH) = C?H??; U = ½(10 10) = 0. The compound is saturated.
C?H?O ? C?H6; U = ½(6 6) = 0
For C?H?6 (benzene), U = ½(14 6) = 4. Any time you get U ? 4, you should suspect the presence of an aromatic ring.
C?H?NO ? C?H?(CH) = C?H?. The corresponding alkane is C?H??. U = ½(14 6) = 4. Aromatic?
C?H??O? ? C?H??; U = ½(14 12) = 1.
C?H??N?Br? ? C?H??(CH)?H? = C?H??; U = ½(18 16) = 1.
Our Company
-
- essayanswerscentre will be listed as ‘Writing Help’ on your bank statement.