can i substitute sour cream for buttermilk in a cupcake recipe?

Yes:
For recipes, a substitute for buttermilk can be made by adding 1 tablespoon of lemon juice or vinegar or 1 3/4 teaspoons cream of tartar to each cup of regular milk. The soured milk should be allowed to sit for ten minutes before being used.[4]

A low-fat substitute can be made by mixing equal parts of skim milk and low-fat yogurt or sour cream.[5]

also from cdkitchen
Buttermilk Substitute

For each 1 cup buttermilk called for in a recipe, use 1 cup plain yogurt or sour cream;
OR
1 tablespoon lemon juice or vinegar plus enough milk to make 1 cup;
OR
1 cup milk plus 1 3/4 tablespoons cream of tartar;
OR
1/4 cup buttermilk powder and 1 cup water.

Sour cream doesn’t have enough acid to get the lift you want. But you can mix a half cup of yogurt with a half cup of milk.