Chapter 3: Functional Groups/Alkanes and Cycloalkanes

Transcription

1 hapter 3: Functional Groups/Alkanes and ycloalkanes ther functional groups Thiols R-S (skunk and additive to natural gas) Nitro R-N 2 thers like imine, enamine, sulfonate, phosphonate.

2 Identify Functional Groups: Taxol (anticancer). rganic hemistry Interactive Notes by N 3 3 Mifepristone (RU 486) 3 3 N Strychnine N 3 3 N Tetradotoxin puffer fish poison Erythrosine - Red #3 N N 2 + I I N I I 2

3 rganic hemistry Interactive Notes by Alkanes: Pretty inert hydrocarbons Straight hain Saturated ydrocarbons Name Molecular Structural Number of Boiling Formula Formula Isomers Point ( o ) Methane Ethane Propane Butane Pentane ( 2 ) exane ( 2 ) eptane ( 2 ) ctane ( 2 ) Nonane ( 2 ) Decane ( 2 ) Note these trends. The names are weird up to 4 and normal greek prefixes after. The formulas and structures of these alkanes increase uniformly by 2 These formulas all fit the formula n 2n+2 the highest possible / ratio Since the / ratio in these compounds is at a maximum, we call them saturated. Isomers result from different arrangements of molecular framework that are composed from the same molecular formula. For example, saturated arrangement of 4 carbons give two possible structures. Draw these as line structure drawings. 5 carbons: Draw these as line structure drawings Practice: Draw all five of the 6-carbon isomers. It helps if you name them. 3

4 rganic hemistry Interactive Notes by Alkyl Groups-Substituents Name Formula ondensed Formula IUPA Name omments Methyl * Methyl Methyl Ethyl * Ethyl 1 0 Propyl Isopropyl -( 3 ) 2 Butyl * Propyl * 3 (1-methylethyl)- 2 0 Branched 3 2 * Butyl (2-methylpropyl) 1 0 Branched Isobutyl - 2 ( 3 ) 2 sec-butyl -( 3 ) * 2 2 * 3 3 (1-methylpropyl) 2 0 tert-butyl -( 3 ) 3 3 * (1,1-Dimethylethyl) Systematic Naming The IUPA rules. Steps: Find the longest chain. Groups attached to the parent chain are called substituents and are named based on the number of carbons in the longest chain of that substituent, and are numbered using the number of the carbon atom on the parent chain to which they are attached. If the same substituent occurs more than once in a molecule, the number of each carbon of the parent chain where the substituent occurs is given and a multiplier is used to indicate the total number of identical substituents; i.e., dimethyl... trimethyl... tetraethyl..., etc. 4

5 rganic hemistry Interactive Notes by Numbering of the carbons in the parent chain is always done in the direction that gives the lowest number to the substituent which is encountered first, or, the lowest number at the first point of difference. If there are different substituents at equivalent positions on the chain, the substituent of lower alphabetical order is given the lowest number. In constructing the name, substituents are arranged in alphabetical order, without regard for multipliers. When these descriptors are used in an IUPA name, iso is alphabetized normally; the hyphenated prefixes, however (sec- and tert-) are disregarded when alphabetizing. A more systematic method for the nomenclature of side-chains involves identifying the longest chain in the substituent, numbering the substituent from the point of attachment to the parent, and indicating side-chains on the substituent using the standard method described for simple alkanes. The name is enclosed in parenthesis to indicate that the numbering corresponds to the local side-chain, not the parent chain. Thus: an isopropyl side-chain can also be named (1-methylethyl), a sec-butyl side-chain can also be named (1-methylpropyl), an isopentyl side-chain can also be named (3-methylbutyl), etc. The origin of the prefixes sec- and tert-, given above, rests with an attempt to describe the nature of the branched carbon unit. By definition, a primary carbon is one which is attached to one other carbon atom, a secondary carbon is one which is attached to two, a tertiary carbon is attached to three, and a quaternary carbon is attached to four other carbon atoms; these are often abbreviated as 1, 2, 3 and 4 carbons. 5

6 rganic hemistry Interactive Notes by Figures and much description above from Try these wacky examples. Practice: Name these 614 isomeric alkanes. Petroleum Distillation A complete story of petroleum distillation can be read at the ow Stuff works web site: Another good source written for chemical engineers can be found at. Which Fraction to Make? Various fractions are more important at different times of year. During the summer driving months, the public consumes vast amounts of gasoline, whereas during the winter more fuel oil is consumed. These demands also vary depending upon whether you live in the frigid north, or the humid south. Modern refineries are able to alter the ratios of the different fractions to meet demand, and maximize profit. 6

7 rganic hemistry Interactive Notes by Fractions btained from rude ils Fraction omposition of carbon chains 7 Boiling range ( o ) Percent of crude oil Natural Gas 1 to 4 Below 20 10% Petroleum ether (solvent) 5 to 6 30 to 60 10% Naphtha (solvent) 7 to 8 60 to 90 10% Gasoline 6 to to % Kerosene 12 to to % Fuel oils, mineral oil 15 to to % Lubricating oil, petroleum jelly, greases, paraffin wax, asphalt 16 to 24 ver % The outcome of burning hydrocarbons. ydrocarbons are burned for heat and gas expansion (IE). Burning anything in the presence of oxygen is called. The general reaction looks like this: omplete combustion x y + 2 x 2 + y/2 2 + heat Assuming the hydrocarbon is octane, 15 gallons (avg tank of gas) burned completely in air makes about 350 lbs of gal (3.8L/gal) (0.7kg/L) (1000g/kg) (1mole/114g) (8moles 2 /1mole 8 18 ) (44g/mole)(1kg/1000g)(2.2#/kg) = 270 lbs. Incomplete combustion: x y + 2 x + y/2 2 + heat

8 ow do we deal with the? rganic hemistry Interactive Notes by What is the reaction of burning coal? What is the octane number? Some of the saturated hydrocarbons between 6 and 12 burn well and some don t. In general, the straight chain hydrocarbons burn poorly with lots of soot. Increasing the branching of the hydrocarbons, increases the reactivity and makes the burning more efficient. n the octane scale: = = 100 The IE needs high octane fuel to avoid afterburning or knocking. The diesel engine does best with poorer octane fuel because heat not a spark is what ignites the fuel. See ycloalkanes Name Substituent Formula ondensed formula Line formula Angles Strain yclopropane yclopropyl 36 yclobutane yclobutyl 48 yclopentane yclopentyl 510 yclohexane yclohexyl 612 ycloheptane ycloheptyl 714 ycloalkane ycloalkyl n2n (2)n Substituted cycloalkanes have 4 naming conventions that differ from alkanes. 1. If substituted, if the substituent is large or complicated then the cycloalkane can be named as a substituent. 2. The numbering starts at a substituted ring atom. 3. The numbering of more than one substituent will depend on picking the lowest possible number combination for the substituents, with the lowest alphabetical substituent taking the lowest #. The direction may be clockwise or counterclockwise. 8

9 rganic hemistry Interactive Notes by Examples of the IUPA Rules in Practice The following two cases provide examples of monosubstituted cycloalkanes. More highly substituted cycloalkanes are named in a similar fashion, but care must be taken in numbering the ring. (4) is-trans Since there can be no rotation around the sigma bonds in the ring, it is possible to have a new kind of isomer. This isomer has the same connectivity but different orientation in 3-D space. We indicate cis trans either with wedges and dashes or with a perspective-line projection technique. onsider 1,2-Dimethylcyclohexane cis -- same side 3 3 trans- opposite sides trans- opposite sides cis -- same side Unsaturation or DI (ydrogen Deficiency Index) n2n. Loss of hydrogen content is called unsaturation. Any time a ring is made, the structure loses 2 s. 9 3

10 rganic hemistry Interactive Notes by Formulas for saturated hydrocarbons are n 2n+2. The first unsaturation would give a formula n 2n. onsider this example: 2 Propane yclopropane 2 2 You can see the relationship between the two structures like this. * * Draw all of the isomers of 5 10 (no alkenes). Draw all of the cis-trans isomers of Dimethylcyclopropane Dimethylcyclobutane Dimethylcyclopentane 10