The target here is a C Corp and a portion of the purchase price is being paid in multi-year installation using seller note. Does the seller have to pay tax on the asset allocation part of the purchase price right away or in the future as and when they receive installations?

For example, assume the purchase price is $1M, and 50% paid as seller note over the next 5 years ($100K each year) and asset/goodwill allocation is $800K/$200K. Will the owner need to pay the tax on full $800K on sale or proportionately now and later as they get paid over the next 5 years?