The Henry Reaction is a base-catalyzed C-C bond-forming reaction between nitroalkanes and aldehydes or ketones. It is similar to the Aldol Addition, and also referred to as the Nitro Aldol Reaction.

If acidic protons are available (i.e. when R = H), the products tend to eliminate water to give nitroalkenes. Therefore, only small amounts of base should be used if the isolation of the β-hydroxy nitro-compounds is desired.

Link provided below to the above henry reactions query .

http://www.almacgroup.com/wp-content/uploads/O201101840KAP1.pdf