Organic Chemistry/Overview of Functional Groups

Introduction The number of known organic compounds is quite large. In fact, there are many times more organic compounds known than all the other (inorganic) compounds discovered so far, about 7 million organic compounds in total. Fortunately, organic chemicals consist of a relatively few similar parts, combined in different ways, that allow us to predict how a compound we have never seen before may react, by comparing how other molecules containing the same types of parts are known to react. These parts of organic molecules are called functional groups. The identification of functional groups and the ability to predict reactivity based on functional group properties is one of the cornerstones of organic chemistry. Functional groups are specific atoms, ions, or groups of atoms having consistent properties. A functional group makes up part of a larger molecule. For example, -OH, the hydroxyl group that characterizes alcohols, is an oxygen with a hydrogen attached. It could be found on any number of different molecules. Just as elements have distinctive properties, functional groups have characteristic chemistries. An -OH group on one molecule will tend to react similarly, although perhaps not identically, to an -OH on another molecule. Organic reactions usually take place at the functional group, so learning about the reactivities of functional groups will prepare you to understand many other things about organic chemistry. Memorizing Functional Groups Don't assume that you can simply skim over the functional groups and move on. As you proceed through the text, the writing will be in terms of functional groups. It will be assumed that the student is familiar with most of the ones in the tables below. It's simply impossible to discuss chemistry without knowing the "lingo". It's like trying to learn French without first learning the meaning of some of the words. One of the easiest ways to learn functional groups is by making flash cards. Get a pack of index cards and write the name of the functional group on one side, and draw its chemical representation on the other. For now, a list of the most important ones you should know is provided here. Your initial set of cards should include, at the very least: Alkene, Alkyne, Alkyl halide (or Haloalkane), Alcohol, Aldehyde, Ketone, Carboxylic Acid, Acyl Chloride (or Acid Chloride), Ester, Ether, Amine, Sulfide, and Thiol. After you've learned all these, add a couple more cards and learn those. Then add a few more and learn those. Every functional group below is eventually discussed at one point or another in the book. But the above list will give you what you need to continue on. And don't just look at the cards. Say and write the names and draw the structures. To test yourself, try going through your cards and looking at the names and then drawing their structure on a sheet of paper. Then try going through and looking at the structures and naming them. Writing is a good technique to help you memorize, because it is more active than simply reading. Once you have the minimal list above memorized backwards and forwards, you're ready to move on. But don't stop learning the groups. If you choose to move on without learning the "lingo", then you're not going to understand the language of the chapters to come. Again, using the French analogy, it's like trying to ignore learning the vocabulary and then picking up a novel in French and expecting to be able to read it. Functional groups containing ... In organic chemistry functional groups are submolecular structural motifs, characterized by specific elemental composition and connectivity, that confer reactivity upon the molecule that contains them. Common functional groups include: Sr No. Chemical class Group Formula Graphical Formula Prefix Suffix Example1 Acyl halide Haloformyl RCOX 75px|Acyl halide haloformyl- -oyl halide 75px|Acetyl chlorideAcetyl chloride(Ethanoyl chloride)2 Alcohol Hydroxyl OH 75px|Hydroxyl hydroxy- -ol 90px|methanolMethanol3 Aldehyde Aldehyde RCHO 75px|Aldehyde oxo- -al 75px|acetaldehyde:Acetaldehyde(Ethanal)4 Alkane Alkyl RHn 75px|Alkyl alkyl- -ane 75px|methaneMethane5 Alkene Alkenyl R2C=CR2 75px|Alkene alkenyl- -ene 75px|ethyleneEthylene(Ethene)6 Alkyne Alkynyl RC≡CR' 100px|Alkyne alkynyl- -yne 100px|acetyleneAcetylene(Ethyne)7 Amide Carboxamide RCONR2 75px|Amide carboxamido- -amide 75px|acetamideAcetamide(Ethanamide)8 Amines Primary amine RNH2 75px|Primary amine amino- -amine 75px|methylamineMethylamine(Methanamine) Secondary amine R2NH 75px|Secondary amine amino- -amine 75px|dimethylamineDimethylamine Tertiary amine R3N 75px|Tertiary amine amino- -amine 75px|trimethylamineTrimethylamine 4° ammonium ion R4N+ 75px|Quaternary ammonium cation ammonio- -ammonium 75px|CholineCholine9 Azo compound Azo(Diimide) RN2R' 75px|Azo.pngl azo- -diazene 150px|Methyl orangeMethyl orange10 Toluene derivative Benzyl RCH2C6H5RBn 75px|Benzyl benzyl- 1-(substituent)toluene 75px|Benzyl bromideBenzyl bromide(1-Bromotoluene)11 Carbonate Carbonate ester ROCOOR 75px|Carbonate alkyl carbonate12 Carboxylate Carboxylate RCOO− 75px|Carboxylate 75px|Carboxylate carboxy- -oate 75px|Sodium acetateSodium acetate(Sodium ethanoate)13 Carboxylic acid Carboxyl RCOOH 75px|Carboxylic acid carboxy- -oic acid 75px|Acetic acidAcetic acid(Ethanoic acid)14 Cyanates Cyanate ROCN 75px|Cyanate cyanato- alkyl cyanate Thiocyanate RSCN 75px|Thiocyanate thiocyanato- alkyl thiocyanate15 Ether Ether ROR' 75px|Ether alkoxy- alkyl alkyl ether 75px|Diethyl etherDiethyl ether(Ethoxyethane)16 Ester Ester RCOOR' Ester|75px -oate 75px|Ethyl butyrateEthyl butyrate(Ethyl butanoate)17 Haloalkane Halo RX 75px|Halide group halo- alkyl halide 75px|ChloroethaneChloroethane(Ethyl chloride)18 Hydroperoxide (see organic peroxide) Hydroperoxy ROOH 75px|Hydroperoxy hydroperoxy- alkyl hydroperoxide 75px|Methyl ethyl ketone peroxideMethyl ethyl ketone peroxide19 Imine Primary ketimine RC(=NH)R' 75px|Imine imino- -imine Secondary ketimine RC(=NR)R 75px|Imine imino- -imine Primary aldimine RC(=NH)H 75px|Imine imino- -imine Secondary aldimine RC(=NR')H 75px|Imine imino- -imine20 Isocyanide Isocyanide RNC isocyano- alkyl isocyanide21 Isocyanates Isocyanate RNCO 75px|Isocyanate isocyanato- alkyl isocyanate Isothiocyanate RNCS 75px|Isothiocyanate isothiocyanato- alkyl isothiocyanate 75px|Allyl isothiocyanatAllyl isothiocyanate22 Ketone Ketone RCOR' Ketone|75px keto-, oxo- -one 75px|ButanoneMethyl ethyl ketone(Butanone)23 Nitrile Nitrile RCN 75px|Nitrile cyano- alkanenitrile alkyl cyanide 75px|Benzonitrile Benzonitrile(Phenyl cyanide)24 Nitro compound Nitro RNO2 75px|Nitro nitro-   75px|NitromethaneNitromethane25 Nitroso compound Nitroso RNO 75px|Nitroso nitroso-   75px|NitrosobenzeneNitrosobenzene26 Peroxide Peroxy ROOR 75px|Peroxy peroxy- alkyl peroxide 75px|Di-tert-butyl peroxideDi-tert-butyl peroxide27 Benzene derivative Phenyl RC6H5 75px|Phenyl phenyl- -benzene 75px|CumeneCumene(2-phenylpropane)28 Phosphine Phosphino R3P 75px|A tertiary phosphine phosphino- -phosphane 75px|MethylpropylphosphaneMethylpropylphosphane29 Phosphodiester Phosphate HOPO(OR)2 75px|Phosphodiester phosphoric acid di(substituent) ester di(substituent) hydrogenphosphate DNA30 Phosphonic acid Phosphono RP(=O)(OH)2 75px|Phosphono group phosphono- substituent phosphonic acid 75px|Benzylphosphonic acidBenzylphosphonic acid31 Phosphate Phosphate ROP(=O)(OH)2 75px|Phosphate group phospho- 75px|Glyceraldehyde 3-phosphateGlyceraldehyde 3-phosphate32 Pyridine derivative Pyridyl RC5H4N75px|4-pyridyl group 75px|3-pyridyl group 75px|2-pyridyl group4-pyridyl(pyridin-4-yl) 3-pyridyl(pyridin-3-yl) 2-pyridyl(pyridin-2-yl) -pyridine 75px|NicotineNicotine33 Sulfide RSR' 75px|Sulfide group di(substituent) sulfide 75px|Dimethyl sulfideDimethyl sulfide34 Sulfone Sulfonyl RSO2R' 75px|Sulfonyl group sulfonyl- di(substituent) sulfone 75px|Dimethyl sulfoneDimethyl sulfone(Methylsulfonylmethane)35 Sulfonic acid Sulfo RSO3H 75px|Sulfonyl group sulfo- substituent sulfonic acid 75px|Benzenesulfonic acidBenzenesulfonic acid36 Sulfoxide Sulfinyl RSOR' 75px|Sulfinyl group sulfinyl- di(substituent) sulfoxide 75px|Diphenyl sulfoxideDiphenyl sulfoxide37 Thiol Sulfhydryl RSH 75px|Sulfhydryl mercapto-, sulfanyl- -thiol 75px|EthanethiolEthanethiol(Ethyl mercaptan) Note: The table above is adapted from the Functional Groups table on Wikipedia. Combining the names of functional groups with the names of the parent alkanes generates a powerful systematic nomenclature for naming organic compounds. The non-hydrogen atoms of functional groups are always associated with each by covalent bonds, as well as with the rest of the molecule. When the group of atoms is associated with the rest of the molecule primarily by ionic forces, the group is referred to more properly as a polyatomic ion or complex ion. And all of these are called radicals, by a meaning of the term radical that predates the free radical. The first carbon after the carbon that attaches to the functional group is called the alpha carbon. Alcohol containing two hydroxyl groups are called glycols. They have both common names and IUPAC names. Mnemonics for Functional Groups These are possible mnemonics for the common functional groups. Vowels: Remember the vowels "A", "E", and "Y" for Alkane, Alkene, and Alkyne. Alkanes have only single covalent bonds. Alkenes have at least one double bond. Alkynes have at least one triple bond. The letters "I", "O", and "U" are not used. Furthermore, "O" and "U" would result in awkward pronunciations. Alcohol: Look for the "C-O-H" in "Alcohol." Ether: Ethers were anesthetics used in the 1800s. Dr. Kellogg also lived at the same time. Corn Flakes are made by Kellogg's. A rooster or cock (C-O-C) is the cornflake mascot. Or, think there is a C on "either" side of the O. Amine: Remember the "N" stands for nitrogen. Aldehyde: This sounds like "Adelaide," the Australian city. Australia is at the end of the Asian islands, and aldehydes are at the end of the hydrocarbon chain. The "Y" indicates a C=O double bond. Ketone: Imagine the diagonal strokes of "K" forming the C=O double bond. File:Ketone_Functional_Group_Mnemonic_K.png Carboxylic Acid: "Box" stands for boxed wine or C-O-H, alcohol. The "Y" indicates a C=O double bond. Ester: This sounds like "Estelle" George Costanza's mother in the TV show Seinfeld. George's nickname was Koko or Coco. So think of O=C-O-C. Amide: Amine with a "D". D for double.