Chem 201/Beauchamp Topic 4, Bare Bones Nomenclature 1 Organic chemistry requires a language that is precise, concise and systematic. Not only do we have to communicate in the written and oral manner, but we must catalogue and store our information in a manner that allows us to retrieve it when searching through the literature. With the explosion of information that is occurring in our time, this becomes more important with each passing day. As a foreign language, organic is relatively simple. But as a scientific language, organic is probably more complicated than in any other science (I’m considering organic and biochemistry as a part of the same language). To our benefit, organic is also probably more organized than any other scientific language. Our nomenclature topic covers about 20 functional groups of organic chemistry. A few more are listed for reference purposes and we will not cover many additional, but less frequently used functional groups. While common names are not stressed in these topics, there are a few that any student of organic chemistry should be familiar with. These will be given in the relevant sections. Don’t be intimidated by these trivial names. They are included so you have a list of the more common examples (for consultation, not for memorization). A few aromatic derivatives (substituted benzene derivatives, etc.) are also included in the relevant functional group sections and at the end. If you have questions as you work through this chapter, visit an office hour for clarification. My hope is that you will be able to speak "basic organic" after finishing these pages. This nomenclature topic has been written with the goal that you can teach yourself too. The following sequences of rules should usually produce an acceptable name for commonly encountered organic compounds. Accessible guidelines to a more complete strategy of nomenclature are provided in Section C of the CRC “Handbook of Physics and Chemistry”. An even more complete compilation of rules of organic nomenclature is provided in “A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations, 1993”, (IUPAC = International Union of Pure and Applied Chemistry). As we proceed through organic chemistry we will often focus our interest on a limited portion of a structure when the remainder of the structure is not important to the topic of discussion. Symbolic representations for generic portions of a structure are given below and are commonly used. We will often use these representations in this and the coming chapters. R = any general carbon group (it sometimes includes hydrogen too) Ar = any general aromatic group, (when more specificity than ‘just’ R is desired) The foundation of organic nomenclature requires an ability to name alkanes, alkenes and alkynes. Learning the rules for these groups will be your biggest nomenclature challenge. Many functional group patterns have a prefix (if lower priority) and a suffix (if higher priority) to specify their presence. Numbers on the longest specified chain will identify their locations. It’s all very organized, but it does require practice. As usual in school, you are the only one who can do that. Pencil, paper and your hard work provides the most reliable path to success. I. Nomenclature Rules For Alkanes and Cycloalkanes The following list provides the names for carbon straight chains of various lengths. They must be memorized (through C19 for problems in this book, C11 – C19 is easier than you think). CH methane (C ) 4 1 C15H32 pentadecane (C15) C29H60 nonaicosane (C29) C H ethane (C ) 2 6 2 C16H34 hexadecane (C16) C30H62 triacontane (C30) C H propane (C ) 3 8 3 C17H36 heptadecane (C17) C31H64 hentriacontane (C31) C H butane (C ) 4 10 4 C18H38 octadecane (C18) C32H66 dotriacontane (C32) C H pentane (C ) 5 12 5 C19H40 nonadecane (C19) C33H68 tritriacontane (C33) C H hexane (C ) 6 14 6 C20H42 icosane (C20) C34H70 tetratriacontane (C34) C H heptane (C ) 7 16 7 C21H44 henicosane (C21) C35H72 pentatriacontane (C35) C H octane (C ) 8 18 8 C22H46 doicosane (C22) C36H74 hexatriacontane (C36) C H nonane (C ) 9 20 9 C23H48 tricosane (C23) C37H76 heptatriacontane (C37) C H decane (C ) 10 22 10 C24H50 tetraicosane (C24) C38H78 octatriacontane (C38) C H undecane (C ) 11 24 11 C25H52 pentaicosane (C25) C39H80 nonatriacontane (C39) C H dodecane (C ) 12 26 12 C26H54 hexaicosane (C26) C40H82 tetracontane (C40) C H tridecane (C ) 13 28 13 C27H56 heptaicosane (C27) C H tetradecane (C ) 14 30 14 C28H58 octaicosane (C28) Chem 201/Beauchamp Topic 4, Bare Bones Nomenclature 2 Basic Steps to Name an Alkane 1. Locate the longest carbon chain present. This becomes the parent name. Make sure to check at each branch point for the longest chain path. (Unless it is obvious, count at each branch point through all possible paths.) Where is the longest chain? (R = substituent branch) incorrect 2 R 1 3 4 10 R 4 6 8 10 12 2 6 8 5 7 9 11 1 3 5 7 9 This chain is longer with 12 Cs so we pick this one. This chain is 10Cs long. If there are several branches radiating out from a central carbon, you can count how long those branches are and use the longest two plus the central carbon and add them all together. 4 4 3 = a central carbon position 4 2 5 These two branches are 3 1 3 equivalent in length, but 6 the lower one is chosen 3 1 5 4 2 2 4 These two branches are equivalent because it has more 1 3 5 2 and because they are longest must branches on it. It must 4 4 3 6 be part of the longest chain. Either also be part of the longest 3 chain. 4 one can be used. 4 4 = part of the longest chain longest chain = 5 + 6 + 1 = 12 parent name = dodecane Number the longest chain from the end nearest a branch point or first point of difference. (The lowest first branch number decides which end of the chain you number from in an alkane.) incorrect 2 What end do you number from? 11 1 3 12 10 R on C R on C4 9 7 5 R 4 6 8 10 12 R 9 3 1 5 7 9 11 8 6 4 2 A lower number for the substituent branch, R, is preferred. C4 is better than C9 so number from the left end. The number will be used to specify the position of the alkyl branch If additional branches are present, the lowest number of the first branch determines the numbering direction on the longest chain. 11 C3 branch is lower than C4 branch 12 10 The direction of the numbering is reversed because the new branch would get a lower number, C , at the first point of difference, than 9 7 5 3 R 3 1 C if the numbering occurred from the opposite direction. 8 6 4 2 4 2. When an alkane portion is present as a substituent or branch (i.e. it is not part of the longest carbon chain) one drops the -ane suffix of a similar length alkane and adds the suffix -yl. Alkane becomes alkyl when it is a substituent; (ethane eth + -yl ethyl.) These substituent names are placed in front of the parent name, as Chem 201/Beauchamp Topic 4, Bare Bones Nomenclature 3 prefixes, with their designating numbers immediately in front of them. Use the numbers obtained from rule 2 to show the location(s) of any substituent(s) or branch(es). Each substituent gets a number, even if it is identical to another substituent and on the same carbon. Hyphens are used to separate the numbers from the letters. Separate substituent position numbers from one another with commas (if the numbers are adjacent). The substituents are listed in alphabetical order. The numerical prefixes (see rule 3) do not count in deciding the alphabetical order (unless they are inside parentheses). 11 There are three one carbon branches on C3, C5 and C9 12 carbons and two two carbon branches, both on the C8 10 substituents carbon. The first branch at C3 determines the direction 3-methyl of numbering because it generates the lowest possible 5-methyl number at the fist point of difference. 9 7 5 3 1 8 6 4 2 8-ethyl 8-ethyl 1C branch = methyl 7C branch = hyptyl 2C branch = ethyl 8C branch = octyl 9-methyl 3C branch = propyl 9C branch = nonyl 4C branch = butyl 10C branch = decyl 5C branch = pentyl 11C branch = undecyl parent name = dodecane 6C branch = hexyl 12C branch = dodecyl 3. For identical substituents, use the prefixes di-, tri-, tetra-, penta-, hexa-, etc. to indicate 2, 3, 4, 5, 6, etc. of these substituents. These prefixes are not considered in deciding the alphabetical order of each substituent (unless inside parentheses). 11 12 substituents 10 3-methyl 5-methyl 8,8-diethyl-3,5,9-trimethyldodecane 9 7 5 3 1 8-ethyl 8 6 4 2 8-ethyl 9-methyl parent name = dodecane 4. With two or more possible longest chains of identical length, choose as the parent name the one with the greater number of substituents. This will produce simpler substituent names. 7-butyl Number from the right because These two branches are 9-propyl the first branch appears at C2. equivalent in length, but 11 5-methyl the lower one is chosen 12 because it has more 10 branches on it. 2-methyl 9 7 5 3 These two branches are equivalent. 8 6 4 2 Either on can be used. 1 10-methyl The substituent alphabetical order is are: 8,8-diethyl b > e > m > p (don't count "d" of di- or "t" of tri-).