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Incoming links: Acid-catalysed acetal hydrolysis
D is , and E is . D results from transesterification; E results from acid-catalysed acetal hydrolysis.
For D, methoxide attacks the ester carbonyl carbon and moves the carbonyl pair to oxygen. Collapse of the tetrahedral reaction intermediate reforms C=O and expels ethoxide. Proton transfer with the methanol solvent regenerates methoxide. Excess methanol favours replacement of the ethyl ester by a methyl ester; the dimethyl acetal survives these basic conditions.
For E, protonate one acetal oxygen, then break its C–O bond with the pair going to oxygen, releasing methanol and forming an oxocarbenium ion. Water attacks that carbon. Deprotonation gives a hemiacetal; protonation of its remaining methoxy oxygen permits loss of a second methanol. The hydroxyl oxygen's lone pair forms C=O during this loss, and deprotonation gives the aldehyde, regenerating the acid catalyst.
Original products and electron-flow steps for transesterification and acid-catalysed acetal hydrolysis
. Details. 
The spectroscopy is consistent with these products. D has one ester carbonyl near and six carbon-13 NMR environments: acetal CH, two distinct chain sites, carbonyl, ester , and the two equivalent acetal groups. Thus seven carbon atoms give six resonances. E has separate ester and aldehyde carbonyl bands, approximately and , and six distinct carbon atoms: two carbonyls, two chain methylenes and the two ethyl carbons.