Final answer:
Capsaicin is the compound that causes the 'hot' sensation in chilies by activating heat-sensitive receptors in the mouth.
Step-by-step explanation:
The main hot substance found in chili is Capsaicin. Capsaicin is a compound that provides the heat sensation in hot peppers. This molecule is structurally comprised of functional groups such as phenol, ether, amide, and alkene. When consumed, capsaicin interacts with receptors in the mouth that are also sensitive to heat, causing the perception of spiciness or heat. Specifically, capsaicin activates the transient receptor potential cation channel subfamily V member 1 (TRPV1), which typically responds to heat, resulting in the characteristic 'hot' sensation experienced when consuming spicy foods.