Generally, molecules meeting this specification have molecular weights of less than 310. Flavors affect both the sense of taste and smell, whereas fragrances affect only smell. Flavors tend to be naturally occurring, and the term fragrances may also apply to synthetic compounds, such as those used in cosmetics.Aroma compounds can naturally be found in various foods, such as fruits and their peels, wine, spices, floral scent, perfumes, fragrance oils, and essential oils. For example, many form biochemically during the ripening of fruits and other crops. Wines have more than 100 aromas that form as byproducts of fermentation. Also, many of the aroma compounds play a significant role in the production of compounds used in the food service industry to flavor, improve, and generally increase the appeal of their products.An odorizer may add a detectable odor to a dangerous odorless substance, like propane, natural gas, or hydrogen, as a safety measure.

Aroma compounds classified by structure

Esters

Linear terpenes

Cyclic terpenes

Note: Carvone, depending on its chirality, offers two different smells.

Aromatic

Amines

Other aroma compounds

Alcohols

Furaneol (strawberry)

1-Hexanol (herbaceous, woody)

cis-3-Hexen-1-ol (fresh cut grass)

Menthol (peppermint)

Aldehydes

High concentrations of aldehydes tend to be very pungent and overwhelming, but low concentrations can evoke a wide range of aromas.

Acetaldehyde (ethereal)

Hexanal (green, grassy)

cis-3-Hexenal (green tomatoes)

Furfural (burnt oats)

Hexyl cinnamaldehyde

Isovaleraldehyde – nutty, fruity, cocoa-like

Anisic aldehyde – floral, sweet, hawthorn. It is a crucial component of chocolate, vanilla, strawberry, raspberry, apricot, and others.

Cuminaldehyde (4-propan-2-ylbenzaldehyde) – Spicy, cumin-like, green

Esters

Fructone (fruity, apple-like)

Ethyl methylphenylglycidate (Strawberry)

alpha-Methylbenzyl acetate (Gardenia)

Ketones

Cyclopentadecanone (musk-ketone)

Dihydrojasmone (fruity woody floral)

Oct-1-en-3-one (blood, metallic, mushroom-like)

2-Acetyl-1-pyrroline (fresh bread, jasmine rice)

6-Acetyl-2,3,4,5-tetrahydropyridine (fresh bread, tortillas, popcorn)

Lactones

gamma-Decalactone intense peach flavor

gamma-Nonalactone coconut odor, popular in suntan lotions

delta-Octalactone creamy note

Jasmine lactone powerful fatty-fruity peach and apricot

Massoia lactone powerful creamy coconut

Wine lactone sweet coconut odor

Sotolon (maple syrup, curry, fenugreek)

Thiols

Thioacetone (2-propanethione) A lightly studied organosulfur. Its smell is so potent it can be detected several hundred meters downwind mere seconds after a container is opened.

Allyl thiol (2-propenethiol; allyl mercaptan; CH2=CHCH2SH) (garlic volatiles and garlic breath)

(Methylthio)methanethiol (CH3SCH2SH), the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice

Ethanethiol, commonly called ethyl mercaptan (added to propane or other liquefied-petroleum gases used as fuel gases)

2-Methyl-2-propanethiol, commonly called tert-butyl mercaptan, is added as a blend of other components to natural gas used as fuel gas.