A functional group is what we call specific groupings of certain atoms within molecules that have their own characteristic properties. Show
Here are some of the most commonly encountered functional groups. Note that “R” is a placeholder for a generic carbon substituent. A second group of slightly less commonly encountered functional groups are here. This is by no means an exhaustive list, but it’s at least a good start. In the beginning of the course, being presented with a list of 20-25 functional groups to remember might seem like a lot. And it probably is! The good news is that you’ve already learned a lot of functional group names without trying too hard. Do these names sound familiar? Propane. Tylenol. Ibuprophen. Testosterone. Dopamine. Learning functional groups will be a matter of connecting those names to general structures. Another good way to get to know functional groups is to think about the relative electronegativities of the elements in each group. That will help you understand their properties and help you think about how they behave in chemical reactions. 2. Alkanes, Alkenes, Alkynes, and Aromatic RingsThe hydrocarbon functional groups are very non-polar and tend to be extremely weak acids. In hydrocarbons, the only types of intermolecular interactions are London dispersion forces and their boiling points tend to be quite low, relative to molecules containing more polar functional groups. Alkanes are hydrocarbons containing no multiple bonds. Alkane substituents are called alkyl groups, which refers to alkanes lacking a C-H bond such as methyl, ethyl, or propyl.
Alkenes are hydrocarbons with one or more carbon-carbon double bonds.
Alkynes contain a carbon-carbon triple bond.
Benzene rings are six-membered rings containing 3 double bonds. Benzene rings are common in nature due to a property called aromaticity (nothing to do with its smell) that make them unusually stable. Can also be drawn as a hexagon with a circle.
Draw examples of alkanes, alkenes, alkynes, and aromatic rings. Click to FlipThe following molecules lack substituents. Draw them in. Click to Flip3. Alcohols, Ethers, Amines, Thiols, Alkyl HalidesThese functional groups is considerably more polar due to the greater difference in electronegativities between the bonding atoms. Stronger intermolecular forces are present in these functional groups due to the dipole-dipole interactions. Additionally, alcohols and amines are capable of hydrogen bonding, which further increase boiling points. Alcohols R-OH contain carbon bonded to the hydroxyl group -OH.
Ethers R-O-R are oxygen atoms flanked by two bonds to carbon.
Alkyl halides have functional group R-F, R-Cl, R-Br, R-I where R is an alkyl group.
Amines contain the functional group -NH2, -NHR, or NR2 where R is a hydrocarbon.
Thiols (mercaptans) R-SH are the sulfur-containing cousins of alcohols.
Draw examples of each of these functional groups. Click to FlipDraw in the functional groups of these famous molecules. Click to Flip4. Aldehydes, Ketones, Carboxylic Acids, EstersThe C=O group is referred to as the carbonyl group. The C=O bond is strongly polarized towards oxygen and the carbon bears a partial positive charge. Carbonyls are found in aldehydes, ketones, esters, and carboxylic acids. Aldehydes RCHO have C=O bonded to carbon and to C-H
Ketones RC(O)R have C=O bonded to two carbons.
Carboxylic Acids RCOOH have a carbonyl bonded to -OH. They are distinct functional groups from alcohols.
Esters RCOOR are similar to carboxylic acids, except the O-H bond is replaced with an O-C bond.
Draw an example of an aldehyde, ketone, carboxylic acid, and ester Click to FlipDraw in the functional group for these prominent molecules. Click to Flip5. Amides, Acid Halides, Anhydrides, NitrilesThere are actually quite a few important functional groups containing carbonyls. These functional groups are all considered to be derived from carboxylic acids, as they can be obtained through replacement of OH with various groups. (Nitriles might not appear to be related to carboxylic acids at first glance, but they can actually be converted into amides through dehydration.) Amides contain a carbonyl carbon attached to an amino group.
Acid Halides have -OH replaced with F, Cl, Br, or I. Anhydrides contain an oxygen flanked by two carbonyls. Distinct from esters.
Nitriles don’t look like carboxylic acid derivatives at first, but they can be formed via the dehydration of amides.
Draw in examples of an amide, acid halide, anhydride, and nitrile. Click to FlipFill in the functional groups of these famous molecules. Click to Flip6. Miscellaneous: Epoxides, Thioethers, Nitro, Imine, AzideNo common thread here; just a few more prominent functional groups worth knowing. Technically, Epoxides are ethers, but since they participate in a number of reactions that ethers generally don’t , they deserve their own category. Thioethers (sulfides) are the sulfur equivalents of ethers. Dimethyl sulfide is the most commonly encountered example. Nitro groups are strongly electron-withdrawing. Nitromethane, a solvent, is the simplest example of a nitroalkane. Imines are the nitrogen-containing equivalents of aldehydes and ketones. Azides pop up from time to time. The “A” in the anti-HIV drug AZT stands for azido. Draw in the functional groups in these molecules. Click to Flip7. That’s Probably Enough For NowOf course there are more functional groups that you will encounter, but this list should be sufficient for most students in an Org 1 course. Past a certain point, the law of diminishing returns starts to apply. The sooner you try to get beyond knowing the name of a functional group and start to apply concepts like electronegativity and resonance, the more “alive” each of these functional groups will seem to you. What is a nonpolar group?In a nonpolar molecule, there are no positive or negative poles formed in the molecule. Any charges are distributed evenly across the molecule. Nonpolar molecules are generally symmetrical, like the tetrahedral molecule carbon tetrachloride. Another example is boron trifluoride, which is trigonal planar.
Are all functional groups are polar?Functional groups can sometimes be classified as having polar or non-polar properties depending on their atomic composition and organization.
How do you tell if a functional group is hydrophilic or hydrophobic?Functional groups are usually classified as hydrophobic or hydrophilic depending on their charge or polarity. An example of a hydrophobic group is the non-polar methane molecule.
Which functional group is always polar?Hydroxyl is always polar. Carbonyl determines the two groups of sugars. Carboxyl has acidic properties and a carboxyl group is written –COOH.
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