NOMENCLATURE VI BASICS

Transcription

1 NMENLATURE VI This exercise covers the basics of organic nomenclature. It is primarily based upon the IUPA system (the names under IUPA rules are called systematic names). In a few cases there are special names, these special names are the common names and, in general, were in use before the IUPA system was developed. Steps I through VII are basic to all organic nomenclature and you should pay particular attention to these steps. Each new type of organic molecule simply adds one or two extra steps to these seven. nce you have mastered the first basic steps, the rest is much easier. I. hains BASIS In most cases, the root of the name comes from the longest continuous chain ( straight chain ) of carbon atoms in the compound. A straight chain is one that can be traced from one end of the compound to the other with backtracking. Any carbon atoms not a part of this chain are parts of branches. The naming of the straight chain is based upon the number of carbon atoms. This root also serves for branches. No. of 's Root No. of 's Root 1 meth (form) 6 hex 2 eth (acet) 7 hept 3 prop 8 oct 4 but 9 non 5 pent 10 dec Additional information must be added to the appropriate root to complete the name of the compound. The roots form and acet are used in special cases that will be discussed later. In general, these two roots are not true IUPA. II. Suffixes Adding a suffix to the root indicates the type of compound. Each type of compound has its own unique suffix. For most hydrocarbons (compounds containing only carbon and hydrogen) the basic suffixes are: -ane alkane (ydrocarbons with only single bonds) -ene alkene (ydrocarbons with a carbon-carbon double bond) -yne alkyne (ydrocarbons with a carbon-carbon triple bond) Double bonds and triple bonds are examples of functional groups. The importance of functional groups presented later.

2 IIa. yclo ompounds yclo compounds have a prefix. If the straight chain is in the form or a non-aromatic ring, combine the prefix cyclo with the root. For now, a non-aromatic ring will be considered any ring of carbon atoms that does not have alternating single and double bonds. Example yclobutane yclo compounds may occur as cis and trans isomers similar to those in the alkenes covered below. III. Branches If not all the carbon atoms are in a continuous chain, the compound is a branched compound. If there is more than one chain (branched) then look for: a. The longest chain that contains a functional group (see later) b. The longest chain (greatest number of carbon atoms not in branches). Example The following will appear in the next three examples. Longest chain is in boldface 9 's nonane If there are two chains of the same length, pick the one with the most substituents (branches). If there are no branches present sometimes, an n- may be in front of the name of the hydrocarbon portion of the molecule (common name).

3 IV. Numbers Number the longest chain from one end to the other with the following considerations: a. The lowest number goes to any functional group. b. The lowest number(s) go to the branch(es) Example For the above example the numbering of the chain (boldface carbon atoms) would be: Do not alter assigned numbers later V. Name Branches The root for the name of a branch is determined in I above; simply count the number of carbon atoms. The name is finished by adding a -yl suffix to the root. Example In the above example, there are three branches. 2 methyl groups 1 ethyl group a. Arrange the branches alphabetically. b. If there is more than one of a particular type use a prefix also (di-, tri-, tetra-, etc.). This does not alter the arrangement from part a. c. Indicate the position of each branch with a number from step IV. Each branch must get its own number even if it is identical to one already used. Example In the above example this gives: 5-ethyl-2,2-dimethylnonane a. ethyl before methyl b. 2 methyl groups = dimethyl c. three branches = three numbers Separate numbers from other numbers by commas and numbers are separated from letters by a dash.

4 VI. Special Names for Branches ertain branches have special names. Some of these are: isopropyl 3 secondary butyl (or sec-butyl) isobutyl tertiary butyl (or tert-butyl) Note: Be careful on these, it is possible to draw these in many different ways. VII. alides Similar rules apply to the alkyl halides (compounds of,, and one or more halogens-f, l, Br, or I). The halogens are treated exactly the same as branches. Indicate the different halogens as: F fluoro Br bromo l chloro I iodo Nonsystematic names for alkyl halides assume that the hydrocarbon portion of the molecule is a branch upon a halide ion. Example 3 3 l This could be: 2-chloropropane (systematic) or isopropyl chloride (nonsystematic) The preceding steps outline the basic procedures of organic nomenclature covered in this class. The following material extends this basic procedure to compounds containing various additional functional groups. In general, each of these functional groups will be more important than the preceding functional groups. (This will not always be true, but for now assume that it is true.) In nomenclature, numbering of a chain must give the most important functional group the lowest possible number.

5 Alkenes Alkenes are hydrocarbons containing at least one carbon-carbon double bond. The longest chain must contain the = (unless a more important functional group is present). The name will end in an -ene. Use a number to indicate the position of the double bond (lowest possible), with the position of the double bond being indicated by the lowest numbered carbon atom of the double bond. nce numbered do not renumber. Example (ydrogens left out for simplicity-not an acceptable final answer on an exam.) 1-butene (double bond between numbers 1 and 2) NTE: 2-butene (double bond between numbers 2 and 3) 1-butene (Not 3-butene) No numbers are necessary for the double bond in a simple cycloalkene as the double bond is always between carbon atoms 1 and 2. (Numbers would be needed for all double bonds if more than one is present.) Be careful not to mistake an aromatic substance for a cycloalkene. If there is more than one = use a prefix on the -ene 1,4-octadiene (Note each double bond gets its own number) Alkenes may form geometric isomers. There are two general types of geometric isomers: cis and trans. is means on the same side, and trans means on the opposite side. (ycloalkanes may also have cis and trans isomers.)

6 1-butene no cis or trans isomers. ( s always cis and trans) 2-butene cis-2-butene (The methyl groups (or hydrogen atoms) are on the same side of the double bond.) trans-2-butene (The methyl groups (or hydrogen atoms) are across the double bond from each other.) Make sure that only groups directly attached to the doubled bonded carbon atoms are use to determine if a molecule is cis or trans. In addition, if a molecule is not drawn to indicate whether it is cis or trans, it is not necessary to specify which it is. ne alkene has a special (common) name: 2 = 2 (ethylene). There are special names such as this one to learn in addition to the systematic names (ethene in this case).

7 Alkynes Alkynes are hydrocarbons containing a carbon-carbon triple bond. Alkynes follow the same rules as alkenes except that the ending is -yne. There are no cis/trans isomers for alkynes. Example 1-chloro-2-butyne 3 2 l There is one special name: acetylene ( 2 2 ). Aromatics Aromatic compounds contain one or more aromatic rings. For this class an aromatic ring will be indicated by a ring of six carbon atoms connected by alternating single and double bonds (resonating) or a six membered ring with a circle in it. Aromatic compounds are not limited to six membered rings, but only such materials will be a part of this discussion. In most of the cases examined here, the IUPA names are the same as the common names. The simplest aromatic presented here is benzene ( 6 6 ). Benzene has six carbons in a ring each carbon has a single hydrogen. ther compounds form by replacing one or more of the hydrogens. If, for example, replacing one of the hydrogens with chlorine the compound becomes chlorobenzene (the carbon to which the chlorine is attached is automatically number one so no number is needed in the name). Thus naming benzene derivatives is similar to the nomenclature discussed above. If two or more of the hydrogens is replaced each of the replacements needs to have its position indicated by a number (even though one of the numbers must be a one). Thus replacing two of the hydrogens of benzene with bromines gives the formula 6 4 Br 2. There are three isomers with this formula; they are: 1,2-dibromobenzene 1,3-dibromobenzene 1,4-dibromobenzene You should draw each of these and prove to yourself that there are no others. Do not to forget to number around the ring to give the smallest numbers. In many cases, it is possible to use common names for the disubstituted aromatics. The common names use words (or letters) in place of the numbers. The above three dibromobenzenes have the following common names: ortho-dibromobenzene meta-dibromobenzene para-dibromobenzene o-dibromobenzene m-dibromobenzene p-dibromobenzene

8 Either the name or the single letter abbreviation may be substituted for 1.2-, 1,3- or 1,4-. Note: Even when the single letter abbreviation is used, pronounce the entire name when naming the compound. The benzene ring may be a branch. In this case, remove one of the hydrogens and attach the ring to something else. A benzene ring present as a branch is a phenyl group ( 6 5 -). The only other aromatic hydrocarbon covered here is toluene. Toluene forms by replacing a hydrogen from benzene with a methyl group ( ). The carbon with this methyl group is automatically number one (this number one is not in the name). Nomenclature for toluene derivatives is similar to benzene derivatives. Thus, when a hydrogen from one of the ring carbons (not from the methyl) is replaced by, for example, a bromine the following isomers could be formed ( 6 4 Br 3 ): ortho-bromotoluene meta-bromotoluene para-bromotoluene 2-bromotoluene 3-bromotoluene 4-bromotoluene hanges on the methyl carbon of the toluene give a benz root. For example, branching on the methyl carbon ( ) gives a benzyl branch. Derivatives Derivatives are organic compounds containing other elements in addition to carbon, hydrogen and halogens. These other elements are part of functional groups. Functional groups are normally the place where a molecule will react. The functional group normally gets the lowest number when numbering the chain, and it must be part of the longest chain (this is true even when another chain contains more carbon atoms). nly functional groups containing oxygen and/or nitrogen will be considered at this time. For indicating the formulas of various derivatives, it is common practice to use an R to indicate a hydrogen or hydrocarbon part of the molecule. In some cases more than one R may be needed; if this is the case they may be designated R and R etc. xygen Derivatives Alcohols Alcohols or organic compounds where one of the hydrogens has been replaced by a hydroxyl group. The general formula for an alcohol is R-- There are two ways to name alcohols. The IUPA system requires the final -e be removed from the name of the hydrocarbon and an -ol be put in its place. For the common name, the hydrocarbon portion is named as a branch on an alcohol.

9 Example 1-propanol or n-propyl alcohol Multiple numbers and prefixes (di, tri, etc.) are necessary if more groups are present. Example 1,3-propandiol The presence of other groups may complicate the numbering. Example I 3-iodo-2-propen-1-ol 1 = position of alcohol group, there is no room for it in front of the prop. (The alcohol is the most important group present, so it gets the lowest number.) 2 = double bond between 2 and 3. This must be before the prop. 3 = position of I Replacing one hydrogen on an aromatic ring with an gives a phenol. The simplest phenol is the compound phenol ( 6 5 ). The carbon to which the hydroxyl group is attached in number 1. Phenols may look like alcohols, but they often behave differently. If an - replaces one of the hydrogens on the methyl group of toluene the compound is benzyl alcohol.

10 Ethers Ethers are organic compounds where one oxygen is placed between two carbon atoms. This gives the general formula: R--R'. When naming an ether both R and R are named as branches (-yl) suffix and separated placed before the word ether. Example ethyl methyl ether (alphabetical) Example diethyl ether Example ethyl phenyl ether arbonyl Derivatives These are oxygen-containing organics containing a carbonyl group. arbonyl group Aldehydes Aldehydes have the general formula: R R may also be an. The carbonyl carbon must be number 1 so no number is needed. Aldehydes are named similar to alcohols except that an -al suffix is used in place of an -ol suffix. Example propanal (The carbonyl must be number 1.) ommon names use the suffix -aldehyde instead of -al (also, form- and acet- are the preferred roots). Example phenylethanal or phenylacetaldehyde

11 Three special names are important here: Ketones formaldehyde methanal 3 acetaldehyde ethanal 6 5 benzaldehyde benzaldehyde (This is one of the cases where the systematic name is the common name.) Ketones have the general formula: R R' Thus, a minimum of three carbons are needed. Again, as in aldehydes, the carbonyl carbon receives the lowest number. Naming is the same as for alcohols except that an -one suffix is used. There is one special name that you will need to know: 3 3 propanone acetone (Note the acet- root even though three, not two, carbons are involved.) arboxylic Acids The general formula for a carboxylic acid is: R (R may also be an ) The carbonyl is automatically number 1. arboxylic acids are named like alcohols except that the suffix is -oic acid. Special names and IUPA names for the two simplest carboxylic acids are: formic acid methanoic acid 3 acetic acid ethanoic acid

12 Two other important carboxylic acids are benzoic acid ( 6 5 ) and oxalic acid ( = ). The loss of the acidic hydrogen from an acid produces a carboxylate ion. The carboxylate ion is named by replacing the -ic acid with -ate. Example - formate ion methanoate ion Esters 3 - acetate ion ethanoate ion The general formula for an ester is: R R' (R may be a hydrogen, but not R) The naming of an ester relates to how an ester forms. Esters form by the reaction of an acid and an alcohol. In the general formula, R, is from the alcohol (named as a branch), and, R', is from the acid (named as a carboxylate ion). Example acetic methyl methyl acid alcohol acetate ethanoic methanol methyl acid ethanoate This is condensation reaction. In a condensation reaction, splitting out a small molecule and joining two groups.

13 Nitrogen Derivatives There are two major types of nitrogen derivatives: amines and amides. Amines are similar to alcohols or ethers except that N replaces. Amides are similar to esters except that N replaces the noncarbonyl. Amines Amines are ammonia derivatives just as alcohols are water derivatives. In these compounds replace one or more of the hydrogens by an organic group. IUPA nomenclature uses an -amine suffix, common nomenclature names all of the organic groups as branches. In the IUPA system, label additional groups on the nitrogen with an N. Do not forget, only the carbon atoms get numbers. Example 3 2 -N 2 ethylamine ethanamine 3 2 -N- 3 ethylmethylamine (alphabetical) N-methylethanamine If a -N 2 group is attached to a larger molecule, and it is not to be named as an amine, this group is called an amino group. A benzene ring with one of the hydrogens replaced by an amino group ( 6 5 N 2 ) is aniline. If one of the carbons, and its attached hydrogen, from benzene is replaced by a nitrogen ( 5 5 N) pyridine forms. Pyridine is still aromatic and the nitrogen occupies position number 1. Amides The general formula for and amide is: R R' N R" (Any, or all, of the R s may be hydrogen) Amides form in a method analogous to esters (even though the exact reaction will not work directly). Amide nomenclature is therefore similar to ester nomenclature. Naming amides is done by dropping the -oic acid (or -ic acid) from the name of the corresponding acid and replacing it with -amide. Indicate substituents on the nitrogen with an N.

14 Example 3 N 3 N-methylacetamide or N-methylethanamide N 3 3 N,N-dimethylformamide or N,N-dimethylmethanamide

15 PRATIE SET VI-1 Draw the structure of each of the following: (For additional practice do both the condensed and structural formulas) 1. 2-methylhexane 2. 2,3,4-trimethylpentane 3. 1-ethyl-3-methylcyclohexane 4. 1-chloro-2-butene 5. 1,5-dibromocyclohexene 6. 5-methyl-1-hexyne 7. isopropyl alcohol 8. 4-phenyl-2-pentanol 9. 3-bromophenol 10. tert-butyl phenyl ether 11. propanal methylbenzaldehyde pentanone hexenoic acid 15. potassium acetate 16. ethyl acetate 17. Dimethyl ethyl amine 18. methyl propanate 19. Benzene 20. Toluene

16 PRATIE SET VI-2 Draw the structure of each of the following: (For additional practice do both the condensed and structural formulas) 1. isopropyl bromide 2. 2,3,5-trimethyl-4-propylheptane 3. 2-methylcyclohexanol 4. 3-chloro-1-octene 5. 4,4-dimethyl-1-pentyne 6. 3-phenyl-2-propen-1-ol 7. diethyl ether 8. 3,5-dimethylcyclohexene 9. butanone methylpropanal methylhexanoic acid 12. methyl p-chlorobenzoate 13. methanamine 14. N,N-dimethylacetamide chloropropyne hexene 17. trans-2-pentene methyl-2-heptene chloro-3-methylpentane ethyl-3-methylhexane

17 Name each of the following: PRATIE SET VI = Br-l N N ( 3 ) ( 3-2 ) l 6 4 N 2 (3 names) =

18 PRATIE SET VI-4 Draw and name each of the isomers of the following: l N (do only those containing a carbonyl group) (do only the acids and esters) N (do only the amides) Na