Short answers, pulled from the story.
An aldehyde is an organic compound containing a functional group with a central carbon atom bonded by a double bond to oxygen, a single bond to hydrogen, and a single bond to a carbon or hydrogen substituent. The word was coined by Justus von Liebig as a contraction of the Latin alcohol dehydrogenatus, meaning dehydrogenated alcohol. The central carbon is sp2-hybridized, and the carbon-oxygen bond is about 120-122 picometers long.
Aldehydes occur naturally in trace amounts in essential oils, where they contribute to characteristic odours; examples include cinnamaldehyde, vanillin, and cilantro. Most sugars, known as aldoses, are derivatives of aldehydes that exist in a masked hemiacetal ring form. Retinal, which combines with opsins to form photoreceptors involved in vision, is also a naturally occurring aldehyde.
The silver-mirror test uses Tollens' reagent, prepared by dissolving silver(I) oxide in dilute ammonia solution. An aldehyde reduces the silver ions to metallic silver, which deposits as a shiny mirror film inside the glass vessel. The reagent converts aldehydes to carboxylic acids without attacking carbon-carbon double bonds.
Hydroformylation is the dominant industrial method for preparing aldehydes, conducted on a very large scale. It involves treating an alkene with a mixture of hydrogen gas and carbon monoxide in the presence of a metal catalyst. Butyraldehyde, for example, is made by hydroformylation of propylene, though the process also produces the isomeric isobutyraldehyde as a side product.
Formaldehyde is the most widely produced aldehyde, with about 6,000,000 metric tons made each year. It is mainly used in the production of resins when combined with urea, melamine, and phenol, with Bakelite being a well-known example. It also serves as a precursor to methylene diphenyl diisocyanate (MDI), which is used in making polyurethanes.
Acyclic aldehydes are named by identifying the longest carbon chain containing the aldehyde group and replacing the terminal -e of the parent alkane name with -al; formaldehyde becomes methanal and butyraldehyde becomes butanal. When an aldehyde group is attached to a ring, the suffix -carbaldehyde is used, giving names such as cyclohexanecarbaldehyde. If another functional group takes priority for the suffix, the prefix formyl- designates the aldehyde carbon instead.