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General Chemistry Principles, Patterns, and Applications, 2011

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Name<br />

Formula Molecular Mass (amu) Boiling Point (°C)<br />

n-pentane C5H12 72 36.1<br />

propionaldehyde (propanal) C3H6O 58 48.0<br />

aldehyde<br />

butyraldehyde (butanal) C4H8O 72 74.8<br />

acetone (2-propanone) C3H6O 58 56.1<br />

ketone<br />

methyl ethyl ketone (2-butanone) C4H8O 72 79.6<br />

Aldehydes <strong>and</strong> ketones are typically prepared by oxidizing alcohols (part (a) in Figure 24.14 "The<br />

Oxidation State of Carbon in Oxygen- <strong>and</strong> Nitrogen-Containing Functional Groups"). In their reactions,<br />

the partially positively charged carbon atom of the carbonyl group is an electrophile that is subject to<br />

nucleophilic attack. Conversely, the lone pairs of electrons on the oxygen atom of the carbonyl group allow<br />

electrophilic attack to occur. Aldehydes <strong>and</strong> ketones can therefore undergo both nucleophilic attack (at<br />

the carbon atom) <strong>and</strong> electrophilic attack (at the oxygen atom).<br />

Note the Pattern<br />

Nucleophilic attack occurs at the partially positively charged carbon of a carbonyl functional group.<br />

Electrophilic attack occurs at the lone pairs of electrons on the oxygen atom.<br />

Aldehydes <strong>and</strong> ketones react with many organometallic compounds that contain stabilized carbanions.<br />

One of the most important classes of such compounds are theGrignard reagents, organomagnesium<br />

compounds with the formula RMgX (X is Cl, Br, or I) that are so strongly polarized that they can be<br />

viewed as containing R − <strong>and</strong> MgX + . These reagents are named for the French chemist Victor Grignard<br />

(1871–1935), who won a Nobel Prize in <strong>Chemistry</strong> in 1912 for their development. In a Grignard reaction,<br />

the carbonyl functional group is converted to an alcohol, <strong>and</strong> the carbon chain of the carbonyl compound<br />

is lengthened by the addition of the R group from the Grignard reagent. One example is reacting<br />

cyclohexylmagnesium chloride, a Grignard reagent, with formaldehyde:<br />

The<br />

nucleophilic carbanion of the cyclohexyl ring attacks the electrophilic carbon atom of the carbonyl group. Acidifying<br />

the solution results in protonation of the intermediate to give the alcohol. Aldehydes can also be prepared by reducing<br />

a carboxylic acid group (–CO2H) (part (a) in Figure 24.14 "The Oxidation State of Carbon in Oxygen- <strong>and</strong> Nitrogen-<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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