Ketones (pronounced like "key tone") are organic molecules with the generalchemical formula R1R2C=O where R1 and R2 are alkyl or aromatic (hydrocarbon) substituents. The two R groups may be the same or different and the carbon atom is bound to the oxygen atom with a double bond (the C=O unit is called acarbonyl unit and is highlighted in red in the drawings below). The carbonyl oxygen atom has two lone pairs of electrons which are usually omitted from line drawings. Aldehydes are similar to ketones, but one of the R groups is replaced by a hydrogen atom giving a general formula of HRC=O. Additional Info: According to the International Union of Pure and Applied Chemistry (IUPAC) naming (nomenclature) rules, simple ketones are named by taking the name of the longestacyclic hydrocarbon chain in the molecule, dropping the terminal "e" (if present), and adding the suffix "one". In situations where there are other functional groups that take naming precedence, the ketone may be indicated by the use of "oxo". Certain other ketone-containing substructures have additional naming rules that are beyond the scope of this reference. Under IUPAC nomenclature aldehydes are named by taking the name of the longest acyclic hydrocarbon chain in the molecule, dropping the terminal "e" (if present), and adding the suffix "al", "aldehyde" or "carbaldehyde". In some cases the prefix "formyl" may be used. Two aldehydes are indicated by the suffix "dial". In addition, a number of trivial (traditional) names are still recognized. Aldehydes and ketones are widely used industrial chemicals both as solvents and as chemical intermediates (ingredients for other chemicals). Most can be classified as volatile organic compounds meaning that their vapors may be easily inhaled or ignited. Many ketones and aldehydes are also flammable as liquids and solids. Important note: formaldehyde is an industrially important aldehyde that is used on the billion ton scale. Glutaraldehyde is a "cold sterilent" used widely in the health care industry. Both are potent sensitizers. Exposure to either of these can make you hypersensitive to contact with other chemicals and carries definite health risks. Special rules and regulations have been developed to minimize formaldehyde exposure; See: Further Reading below for more information. Several ketones and aldehydes have been classified as known or likely carcinogens. For example, formaldehyde and acetaldehyde are known carcinogens. Studies are still underway on glutaraldehyde but it appears to have a much lower risk (if any) of carcinogenicity than formaldehyde. Acetone has not been reported to cause cancer. MSDS Relevance: Ketones and aldehydes usually appear in MSDS's in one of two contexts: (1) As incompatible materials. Both are rather reactive classes of chemicals, and undergo a wide range of desirable (and sometimes undesirable) reactions. Ketones and aldehydes are particularly incompatible with concentrated nitric and sulfuric acid mixtures. (2) In discussion of the solubility of the material in various solvents. The polar nature (uneven distribution of electron density) of ketones creates intermolecular alignment between other polar molecules and increases their solubility in other polar materials. Smaller chain ketones and aldehydes can have appreciable solubility in water. Ketones may also be referenced in terms of medical condition called ketosis in which ketones build up in the body. The desirable chemical reactivity properties of aldehydes become undesirable when these chemicals enter your body, so be sure to read the label and MSDS for any ketone or aldehyde-containing materials before use. Take appropriate precautions when working with them - engineering controls such as fume hoods and personal protective equipment (PPE) such as gloves and respirators are a very good idea. See also: Alcohol, Carboxylic Acid, Chemical Formula, Carbon Monoxide, Ketosis, VOC