QUIZ 2. Avg / 25 Stnd. Dev. 5. Wed. Feb pm A-N A-120 O-Z A-203. Sign up for early exam. Not on the list - can t take it

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1 QUIZ Avg..7 / Stnd. Dev. Exam. Wed. Feb pm A-N A-0 O-Z A-0 Sign up for early exam. Not on the list - can t take it

2 IUPAC Rules of Nomenclature There are a vast number of alkanes, certainly several millions, and each unique structure requires a unique name. The nomenclature system used today is based on the number of carbon atoms in straight-chain alkanes. It relies on a "code" to designate each type of molecule or functional group, if one is present. Each carbon atom in the linear chain of an alkane will receive a number if a group or atom is attached to that particular carbon, and its position is identified by that number as part of the name. Groups attached to the straight chain of carbon atoms are called substituents. A hydrocarbon substituent that has sp -hybridized carbon atoms is known as an alkyl group or an alkyl substituent. To accommodate the variations in structure, a set of "rules" has been devised that are universally used to name common organic molecules. The organization that supervises these rules is the International Union of Pure and Applied Chemistry, I.U.P.A.C., or just IUPAC.

3 The Nomenclature CODE The system for naming organic molecules begins with the first twenty straightchain alkanes, C to C 0, which are listed in the table on the next slide. A "code" is required to tell everyone that the molecule is an alkane. The code used is a unique suffix, and for alkanes that suffix is ane. A prefix is added to tell the reader how many carbons are in the alkane chain. A one-carbon unit has the prefix meth-; two-carbons are eth-; three carbons are prop-; four carbons are but-. Five, six seven, eight, nine and ten are derived from the Latin terms: pent-, hex-; hept-, oct-, non-, dec-. For -9 hydrocarbons, the name is the equivalent of +0, +0, +0, etc. The prefixes are undec- (), dodec- (), tridec- (), tetradec- (), pentadec- (), hexadec- (), heptadec- (7), octadec- (), nonadec- (9), and icos- (0). The structures in the table are drawn using the CH (CH ) n CH formulas, which is known as condensed notation.

4 C to C0 Unbranched Alkanes Number of Carbons Structure IUPAC Name CH CH CH CH CH CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) 7 CH CH (CH ) CH CH (CH ) 9 CH CH (CH ) 0 CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) 7 CH CH (CH ) CH CH (CH ) 9 CH CH (CH ) 0 CH CH (CH ) CH CH (CH ) CH CH (CH ) CH CH (CH ) 9 CH CH (CH ) 0 CH methane ethane propane butane pentane hexane heptane octane nonane decane undecane dodecane tridecane tetradecane pentadecane hexadecane heptadecane octadecane nondaecane icosane (eicosane) hentriacontane docosane triacontane tetracontane pentacontane hectane dotricontahectane The prefix that indicates the number of carbon atoms in the longest straight chain is indicated in purple. The suffix -ane indicates that the class name is alkane is shown in green.

5 Rules of Nomenclature: - The fundamental system uses a prefix to give the number of carbons and a suffix to describe the class of molecules (and/or functional group). There are several rules.. Determine the longest, continuous chain of carbon atoms that contains the functional group of highest priority and assign the proper prefix to indicate the number of carbon atoms. Determine the class of compounds to which the molecule belongs and assign the proper suffix. For straight-chain, saturated hydrocarbons the class name is alkane and the suffix is - ane.. For alkanes, determine the longest straight chain present, using a prefix for the number of carbons as in Table., and the suffix -ane. CH (CH ) CH same as CH CH CH CH CH same as pentane CH (CH ) CH same as CH CH CH CH CH CH CH CH same as 7 octane

6 Rules of Nomenclature:. Substituents When the longest unbranched chain has a branch (another group attached), that group or atom is called a substituent. If the substituent has only sp -hybridized carbon and hydrogen atoms, it is called an alkyl group, or an alkyl substituent. There is another rule to cover the name of such compounds.. Alkanes that have carbon groups attached to the longest unbranched chain (called substituents) are known as branched chain alkanes. When that branch is an alkane fragment, it is known as an alkyl group or an alkyl substituent. Alkyl substituents are the carbon "branches" attached to the longest carbon chain. When the substituents are hydrocarbon fragments, they require the same prefix used in Rules - to indicate number of carbon atoms, but a different suffix is required. Branched chain alkanes are named in two parts: the terminal portion of the name of the longest straight chain present in the compound (known as the parent chain), and the name of the group constituting the branch (known as a substituent for a substituting group) or the side chain precedes the name of the parent chain. In the parent alkane, the suffix -ane indicates an alkane, but the -ane is dropped and replaced with -yl to indicate an alkyl substituent.

7 Most Observed Substituents 7 In the table, the carbon atom that serves as the point of attachment for the substituent to the main chain is shown in orange. The prefix for a C-C0 substituent is meth icos as in Rules -. Combining the -yl suffix and the alkane prefixes indicates that a one-carbon substituent is methyl, a two-carbon substituent is ethyl, a three-carbon substituent is propyl, and a fourcarbon substituent is butyl, etc. The suffix -yl above comes from work by J. Liebig and F. Wöhler, who adopted it from the Greek word hyle, which translates to material. Note that the -yl suffix is used in the generic term alkyl (any hydrocarbon substituent) CH CH CH CH CH CH CH CH CH CH (CH ) CH (CH ) CHCH CH CH Structure IUPAC Name Common Name CH methyl ethyl -propyl -butyl -methylethyl -methylpropyl -methylpropyl methyl ethyl n-propyl n-butyl isopropyl isobutyl secondary-butyl (sec-butyl) CH CH CH CH CH -methylbutyl secondary-pentyl CH (CH ) C (CH ) CCH,-dimethylethyl,-dimethylpropyl tertiary-butyl (tert-butyl) isoamyl (isopentyl) In each structure, the highlighted carbon (C) is the point of attachment to the longest continuous chain

8 Nomenclature With One Substituent The IUPAC nomenclature rule states that the numbering sequence is based on the nearest locant, which is the carbon bearing the branch. In other words, the locant is the carbon bearing the substituent. Number the longest linear chain from one end to the other by Arabic numerals, and assign the lowest number to the substituent (the nearest locant). In, the hexane chain is numbered to give the methyl group (the one-carbon alkyl substituent is marked in orange) the lower number. Two possible numbering sequences are possible are shown for, from each end of the molecule. One sequence places the methyl group at C, the other at C. In the former case, C is the nearest locant, and in the latter case C is the nearest locant. The nearest locant at C takes precedent because the lower numbering scheme places the methyl at C. Therefore, the name of is -methylhexane. This point is emphasized by compound, which is a structure that could be numbered in such a way that it would be called -methyldecane. This is incorrect! Compound is actually named -methyldecane due to the requirement that numbering the chain gives the substituent the smaller number (C in is the nearest locant). Note that if one could "pick up" a "-methyldecane" and place it on a model of -methyldecane so that the methyl groups overlap. They are the same. Make a model to test this! longest chain substituent NOT

9 Nomenclature With One Substituent 9 The rule stating that the numbering sequence is based on the nearest locant (lowest number is assigned to the substituent) is reinforced with examples and. In, there is an -carbon chain (octane) with a -carbon substituent (methyl). There are two ways to number the -carbon chain, and the preferred one gives the methyl group a number of. The name of is - methyloctane, and not -methyloctane. Alkane is drawn on the page in such a way that the eye is drawn to an -carbon linear chain, but the longest linear chain is 0, so is a decane. If is a decane, then there is a -carbon substituent, a propyl group. Numbering the 0-carbon-chain to give propyl the lowest number leads to -propyldecane rather than -propyldecane

10 A Cautionary Note 0 The molecule shown is a seven-carbon straight-chain alkane named heptane. Heptane is colored coded in a peculiar manner such that a methyl group is attached to the end of a six-carbon linear chain. Can an alkyl substituent be added to the end of a linear chain? Adding a methyl group to the end of a chain simply extends the linear chain. Do not be fooled! Since the methyl group is on the last carbon, the longest continuous chain is now seven carbons, and this is not -methylhexane, despite the way in which it is drawn. It is heptane. Examine the second structure, which appears to have a six-carbon linear chain with a methyl group drawn at a different angle. The longest linear chain is seven, so it still heptane. Both line drawings represent the same molecule. The angle at which a substituent is attached is not important in the line drawings. Look at the points of attachment to determine the structure of the molecule. If the atoms are the same and the points of attachment are the same, the structures must be identical. CH CH

11 Multiple Substituents When the longest unbranched chain has two or more substituents, there is more than one locant.. In branched hydrocarbons having more than one identical substituent, as in with three methyl groups, name each substituent and assign an Arabic number for the position of each substituent on the longest unbranched chain. This rule assigns the lowest sequence of numbers such that the locant closest to the end of a chain receives the lowest number. There could be two methyl substituents, or three ethyl substituents, etc. The rules state that another prefix is used with the substituent: di- for two, tri- for three, tetra- for four, penta- for five, and hexa- for six identical substituents. 7 7

12 Multiple Substituents In, the first point of difference is identified: the numbers in purple shows a,,-trimethyl sequences, whereas the numbering in green shows a,,7- trimethyl sequence. The lowest number sequence is,, rather than,,7. This is just another way of saying that the preferred numbering sequence begins with the nearest locant for the first methyl group encountered. In, the nearest locant is C rather than C. The longest linear chain is eight, so this is an octane. The closest locant is the methyl group at C, so,,-trimethyl is used. The molecule cannot be named,,-methyloctane? Every substituent must receive a number, even if there are more than one of the same substituent. Since has three methyl groups, it is a trimethyloctane, and the name is,,- trimethyloctane where commas separate the numbers and a hyphen separates the number from the rest of the name. 7 7

13 Multiple Substituents Compound has two methyl groups attached to a decane chain; one at C and one at C. The nearest locant is at C, so is named,-dimethyldecane. For compound, the two nomenclature possibilities are,-dimethyldecane and,9-dimethyldecane. The nearest locant is at C, so the smaller set of numbers is, (rather than,9) and,-dimethyldecane is the correct name for. For, the longest unbranched chain is 7, so it is a heptadecane, with a methyl and an ethyl group. In terms of sequencing the substituents in the name, ethyl will come before methyl, but the nearest locant is for either group. Therefore, it could be -ethyl- -methylheptadecane or -ethyl--methylheptadecane. The rule states that if the same substituent numbers are obtained in either direction, numbering should be in the direction giving the lowest number to the first named substituent. Therefore, 0 is -ethyl--methylheptadecane 7 7

14 Halogens Are Not Functional Groups When a fluorine, chlorine, bromine, or iodine is attached to a carbon chain, the molecule is named to show that a halogen substituent is present. There is no unique suffix for the halogen. Halogen atoms are named as substituents and a halogen substituent is named by dropping the -ine ending of each halogen and replacing it with o-; i.e. fluoro, chloro, bromo, iodo. The other aspects of naming follow the same protocol used for any substituent. I Br 7 Cl The nearest locant is C in 7 and C in. 7 is -iodo--methylheptane and is -bromo--chlorohexadecane. Numbering the substituents is established by determining the nearest locant that gives the lowest set of numbers, as described above. When there are different substituents, they are arranged alphabetically in the name with their appropriate number.

15 Complex Substituents. If a complex substituent is present on the longest continuous chain, count the number of carbon atom in the longest continuous part of that "side chain" and use the proper prefix. The name of a complex substituent is considered to begin with the first letter of its complete name (take the longest chain of the substituent from the point of attachment to the longest unbranched chain, and ignore di-, tri-, etc.)

16 Complex Substituents The group at C, in the box, is a complex substituent. With the rd group, numbering changes. There is a four-carbon linear chain attached to C, and the butyl substituent is numbered, beginning from the point of attachment, and that carbon is labeled C. is a -butyl--ethyl--methylheptadecane. The butyl substituent has methyl substituents. The carbon attached to C is numbered. There are three methyl groups attached, at C and C as the side chain is numbered., so the complex side chain is a,,-trimethylbutyl, which is attached to C of the heptadecane. The final name of is -(,,-trimethylbutyl)--ethyl--methylheptadecane. Complex side chains are named by choosing the longest chain from the point of attachment to the longest linear chain that gives rise to the base name, here heptadecane, numbering the side chain and a inserting the secondary substituents based on that numbering. In n order to set the complex substituent apart from the other substituents, parentheses are used, as in.

17 Complex Substituents There are cases where the molecule contains two or more complex substituents that have the same number of carbons in the longest chain, but they are different. There are three pentyl groups in. This compound is a tripentylicosane, but the secondary substituents are different. At C7 there is a -methylpentyl, there is a -methylpentyl at C and a - methylpentyl group is at C. The rule states that priority for citation is given to that substituent which contains the lowest locant at the first cited point of difference. In this case the -methylpentyl, followed by -methylpentyl, followed by - methylpentyl. The name of is 7-(-methylpentyl)-9-(-methylpentyl)--(-methylpentyl)icosane.

18 Common Names For Substituents The table shows common alkyl substituents with both their IUPAC and common names. A few common names for simple alkyl fragments have been used for many years, and must be learned. The common name for straight-chain fragments such as propyl or butyl adds n-, which means normal-. Therefore propyl becomes n-propyl and butyl is n- butyl. The fragments sec-isopropyl, butyl, tert-butyl and isoamyl are specialized terms. CH CH CH CH CH CH CH CH CH CH (CH ) CH (CH ) CHCH CH CH CH CH CH Structure CH CH CH CH (CH ) C (CH ) CCH Common Name methyl ethyl n-propyl n-butyl isopropyl isobutyl secondary-butyl (sec-butyl) secondary-pentyl tertiary-butyl (tert-butyl) isoamyl (isopentyl) The term tertiary indicates two methyl groups are on the next-to-last carbon, and iso- indicates that one methyl group on the next to last carbon. The term secondary (sec-) indicates one methyl on the second carbon away from the point of attachment, except that (CH ) CH- is known as isopropyl. These terms become unwieldy if there are more than five carbons and are used only for relatively small fragments. The common names are used only for a parent hydrocarbon such as isobutane or tertbutylhexane. In the IUPAC system, the systematic names must be used exclusively (labeled IUPAC name), and common names are not mixed with IUPAC names.

19 Common Names 9 Some alkyl groups are so common that they have common names pre-dating development of the IUPAC rules. One should always use the IUPAC nomenclature. The IUPAC rules indicate that common names should only be used for the parent alkane, and not for substituents. Substituents are named according to the IUPAC rules listed above.,-dimethylethyl is known as a tertiary-butyl group (or tert-butyl).,-dimethylpropyl substituent is called tertiary-amyl where amyl is an old term for pentyl. -methylethyl group is called isopropyl; the term iso- refers to a carbon at the end of the branch chain has one hydrogen, and two methyl groups. The four-carbon -methylpropyl is called isobutyl and the -methylbutyl fragment is called isopentyl (sometimes isoamyl). For a methyl group is attached to the C-carbon of the branch chain, and there are four or more carbons in the substituent, the common term used is secondary- or sec-. -methylpropyl fragment is therefore sec-butyl and the -methylbutyl fragment is secpentyl or sec-amyl.,-dimethylpropyl fragment, which is known as neopentyl Common names should not be mixed with an IUPAC name.