Chapter 20 Organic Chemistry The chemistry of carbon

Chapter 20: Organic Chemistry �The chemistry of carbon compounds. �Mainly carbon and hydrogen atoms. �Many organic compounds occur naturally. �Thousands more can be synthesized by man. 1

Na. Cl versus Butane �Na. Cl, 58. 5 g/mol �Bonding is ionic �M. P. = 801 o. C �B. P. = 1413 o. C �Dissolves in water �Will not burn �C 4 H 10, 58. 1 g/mol �Bonding is covalent �M. P. = -138 o. C �B. P. = 0 o. C �Not soluble in water �Will burn in air 2

Molecular Geometry �There are three hybridization states and geometries found in organic compounds: �sp 3 Tetrahedral �sp 2 Trigonal planar �sp Linear 3

Classes of Organic Compounds Aliphatic Saturated Alkanes Aromatic Unsaturated Cycloalkanes Benzene Ring Alkenes Alkynes 4

Alkanes �“Saturated” hydrocarbons �All C-C single (sigma) bonds �Formula = Cn. H 2 n+2 5

Formulas �Structure is very important in organic chemistry. �Propane = C 3 H 8, chemical formula �Complete structural drawing – shows every single bond. H H H H–C–C–C–H H H H 6

Formulas �Condensed structural drawing collapses the H atoms that are bonded to EACH carbon atom. �CH 3 – CH 2 – CH 3 , condensed formula. �This is how a formula is written. 7

Formulas �The molecule is really NOT linear, though. �The sigma bonds in the alkanes have free rotation. 8

First Ten Alkanes: Base Names 9

Structural Isomers �For four carbons, there are two ways to arrange. �For five carbons, there are three ways to arrange. 10

IUPAC Nomenclature �A name of a compound consists of three parts. �Prefix, Base, and Suffix prefix substituents base suffix longest chain family (how many C’s) 11

IUPAC Nomenclature �A substituent is any group that is attached to the longest chain of carbon atoms. �CH 4 = methane, -CH 3 = methyl �CH 3 = ethane, -CH 2 CH 3 = ethyl �Cl = chloro, Br = bromo, I = iodo 12

IUPAC Nomenclature 1. 2. 3. • Find the longest chain in the molecule. Number the chain from the end nearest the first substituent encountered. List the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached. LEP #1 13

Cycloalkanes �A ring structure can be constructed from alkanes of three or more carbons by removing two hydrogen atoms. �Because they form a geometric shape, a shorthand method for their structure is that shape. �Rings with 5 and 6 carbons are the most stable. 14

IUPAC Nomenclature �For ring structures, a mono-substituted ring does not need a number. �Why? ? ? �For di-substituted ring structures, number starting from the location of one the substituents and then go CW or CCW to give the next one the lowest number. 15

Haloalkanes �A haloalkane is placing a halogen (group 7 A) atom in place of a hydrogen atom. �Naming uses the fluoro, chloro, bromo, and iodo names. �Haloalkanes are used as refrigerants (CF 3 CH 2 F) and anesthetic agents (CF 3 CHCl. Br). 16

Stereoisomerism and Optical Isomerism �Stereoisomers = molecules in which the atoms have the same connectivity, but have a different spatial arrangement. �Geometric = cis / trans (alkenes) �Optical isomers = are two molecules that are non-superimposable. �Optical isomers are much like your hands – they are not superimposable! 17

Chirality �Any carbon with four unique groups bonded to it are said to be chiral. 18

Chirality • If one of the two optical isomers is present, then it will rotate plane-polarized light to the left or to the right. • An equal amount of both isomers will not rotate the light and is said to be a racemic mixture. 19

Chirality �Many important biochemical molecules are chiral. �Many important pharmaceuticals have at least one chiral carbon. �Ex) Ibuprofen Chiral Carbon 20

Properties and Reactions of Alkanes �Alkanes are non-polar and, thus, do NOT dissolve in water. �Alkanes typically have a density of 0. 65 – 0. 70 g/m. L and will float on the surface of water. �Alkanes are relatively unreactive. �They burn in air, though, to produce energy. �Halogenation: CH 3 + Cl 2 21

Alkenes �Called “unsaturated” �Contain at least one C=C double bond �Simplest alkene = C 2 H 4 22

Alkenes �The double bond does not allow for free-rotation. 23

IUPAC Nomenclature �Naming an alkene. 1. Find the longest chain that includes the double bond. Suffix name uses –ene ending. 2. Number the chain so that the double bond gets the lowest numbers (has priority over other substituents). Only four carbons or longer will need a number for the double bond position. Use only the lowest number for start of double bond. 3. Number substituents based on this numbering. 4. Cycloalkenes – the double bond is ALWAYS position #1 and #2. 24

Geometric Isomers �Some alkenes can have geometric isomers due to rigid shape around double bond. �Requires two different sets of groups on each side of the double bond – one large and one small. A B C=C B A �Opposite = trans, Same side = cis 25

Addition Reactions �Alkenes undergo an “addition” reaction by adding a small molecule across the double bond. �Hydrogenation �Halogenation �Hydration 26

Aromatic Hydrocarbons �Benzene, C H , is a ring 6 6 structure like the cycloalkanes. �However, it is very different from the cycloalkanes, whose ring structures are fairly easy to break open. �Benzene is VERY stable and found in many important molecules like aspirin, vanillin, and acetaminophen. �What makes it unique? 27

IUPAC Nomenclature �Mono-substituted benzene needs no number. �Some have special (common) names. �Toluene, Phenol, and Aniline. �Di-substituted benzene rings are numbered like the cycloalkanes. �Substituted toluenes, phenols, and anilines have those groups as the first position. 28

Functional Groups �Addition of atoms like O, N, and S add reactivity and polarity to the alkanes. �Can occur in many different ways. �Will need to know the nomenclature and reactions of some and be able to identify all. �The letter “R” is a generic designation for an alkyl group. 29

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IUPAC Nomenclature �Alcohols get an –ol suffix. �The –OH group MUST have the lowest number – it has priority. �On a cycloalkane, it is carbon #1. �On benzene it is called phenol. 32

Properties of Alcohols �The –OH group can make the molecule soluble in water due to HB force. �C 1 to C 4 are very soluble in water. �More than five carbons, though, is virtually insoluble. �CH 3 – CH 2 – CH 2 - OH long chain is non-polar (dominates) 33

Reactions of Alcohols �Oxidation = loss of two H’s or gain of O. �Depends on primary, secondary or tertiary. �Primary Alcohol Aldehyde Carboxylic Acid �Secondary Alcohol Ketone �Tertiary No Reaction 34

Ethers �An O atom separating two alkyl groups. �R – O – R’ �Oxygen atom is polar, so smaller ones are soluble in water. �CH 3 – CH 2 – O – CH 2 – CH 3 �MTBE 35

Thiols �A sulfur atom – usually with an H attached. �R – SH �CH 3 – CH 2 – SH, Ethanethiol �These compounds smell BAD! �One amino acid has thiol group. 36

Carbonyl Group �Many functional groups contain a C = O group. �Aldehyde = the C = O group is terminal. �R-CHO �CH 3 – CH 2 – C – H O 37

Carbonyl Group �Aldehydes use the –al suffix. �The carbonyl carbon is automatically the first position. �Ketone = the carbonyl group is in the middle of the chain. �Smallest ketone has three carbons 38

Carbonyl Group �Ketones use an –one suffix. �Number is needed for five or more C’s. �Carboxylic Acid = carbonyl group with a hydroxyl group attached. �R – COOH �Are many of the weak acids seen in Ch. 16. 39

Carbonyl Group • Formulas are written differently! • Ex) Acetic Acid 40

Carbonyl Group �Naming acids – use the –oic suffix plus the name acid. �Like aldehydes, the –COOH group is terminal, so it is C #1. �Esters = has both the carbonyl and the ether type O atom. �R – COO – R’ 41

Carbonyl Group �An ester is made by the reaction of an alcohol and a carboxylic acid. �R – C – OH + HO – R’ R – C – O – R’ O O �The –OH and –H produce water. 42

Amine �An amine contains the N atom. �These can be primary, secondary, or tertiary. �R –NH 2 , R 2 –NH , and R 3 –N. �The N group has a lone pair that will accept a proton �Therefore, these are the weak bases from Ch. 16. 43

Amide �Contain the carbonyl group AND the amine group. �R – (C=O) – NH 2 �The N group can also have an R group. �Made by the reaction of a carboxylic acid plus an amine. �Similar to ester reaction. 44

Polymers �A polymer is a long chain of repeating units called monomers. �Monomers are typically small alkenes. �Reaction is called an addition reaction and are referred to as addition polymers �Initiated by organic peroxide, R-O-O-R’, which is split into two fragments, 2 R-O Benzoyl peroxide 45

Common Monomers �CH 2=CH 2, ethylene makes polyethylene. �Two forms – low density and high density �Uses: �CH 2=CHCl, vinyl chloride makes PVC. �Uses: �CH 2=CHCH 3, propene makes polypropylene. �Uses: �CF 2=CF 2, tetrafluoroethene makes Teflon. �Uses: 46

Common Monomers �CH 2=CCl 2, 1, 1 -dichloroethene makes Saran. �Uses: �CH 2=CH(C 6 H 5), phenylethene makes polystyrene. �Uses: �Recycling – uses a series of symbols and numbers to identify the type. 47

Condensation Polymers �Polyurethanes, Nylons, Rayons, etc. are produced using the ester and/or amide reaction. �Monomer units have two functional groups per molecule. �PETE = ethylene glycol + terephthalic acid �Nylon 6, 6 = adipic acid + hexamethylenediamine 48