Flavans are compounds with a 2-phenyl-3,4-dihydro-2\(H\)-1-benzopyran skeleton (1 in flavonoids), that may be substituted, and include flavan-3-ols (compounds derived from 2-phenyl-3,4-dihydro-2\(H\)-1-benzopyran-3-ol skeleton 2) and flavan-4-ones (compounds derived from 2-phenyl-2,3-dihydro-4\(H\)-1-benzopyran-4-one skeleton 3), which are generically designated as flavanols and flavanones, respectively. Compounds derived from 2-phenyl-3,4-dihydro-2\(H\)-1-benzopyran-3,4-diol skeleton 4 are flavan-3,4-diols, designated leukoanthocyanidins because these colourless compounds have their structure derived from that of an anthocyanidin, specifically they are dehydronated 3,4-dihydroxy-1,2,3,4-tetrahydroanthocyanidins.