Is there capital gain exemption on vacant land?

Yes, if the land was adjacent to your main home and was considered part of your home any gain on the sale of the land qualifies for the exemption under IRS rules.

For example, if you buy a farm with a home and 40 acres, and 12 years later you sell off 36 of the 40 acres but keep the home and four acres, the sale of the land qualifies for the exemption because it was part of your main home. If you also sell the main home within two years, then the gain on both sales will need to be combined to determine whether or not the exemption has been exceeded.

See IRS Publication 523.