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Properties
| Aldehydes, like ketones, are polar molecules. The bond angles and
hybridization are the same. They also have dipole-dipole intermolecular bonding. Because
of this, they are held together with greater attraction than you would find with alkanes
of similar size and molecular weight. |
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| Thus they would have slightly higher melting points and boiling points
than comparable alkanes, which have van der Waals bonding. Aldehydes do not have hydrogen
bonding as alcohols do. Therefore, aldehydes have lower melting points and boiling points
than comparable alcohols. (These values are taken from "Organic Chemistry" by
Morrison and Boyd.) |
| No. of C atoms |
alkanes |
aldehydes |
alcohols |
m.p.
°C |
b.p.
°C |
m.p.
°C |
b.p.
°C |
m.p.
°C |
b.p.
°C |
| 1 |
-183 |
-162 |
-92 |
-21 |
-97 |
64.5 |
| 2 |
-172 |
-88.5 |
-121 |
20 |
-115 |
78.3 |
| 3 |
-187 |
-42 |
-81 |
49 |
-126 |
97 |
| 4 |
-138 |
0 |
-99 |
76 |
-90 |
118 |
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| Aldehydes are also soluble in water -- at least the small ones are. The
solubility in water generally decreases as the length or size of the nonpolar portion (the
alkyl part) gets larger. At about five carbon atoms aldehydes are only slightly soluble,
and less so with more carbon atoms.(These values are also taken from "Organic
Chemistry" by Morrison and Boyd.) |
Solubility in water
g/100g water |
| No. of C atoms |
aldehydes |
alcohols |
| 1 |
very soluble |
¥ |
| 2 |
¥ |
¥ |
| 3 |
16 |
¥ |
| 4 |
7 |
7.9 |
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E-mail instructor:
Eden Francis
Clackamas Community College
©2001, 2003 Clackamas Community College, Hal Bender
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