Carbon: Not Just Another Element

Transcription

1 Page III-20-1 / hapter Twenty Lecture Notes arbon: Not Just Another Element hapter 20: The rganic hemistry chapter! hemistry 222 Professor Michael Russell rganic hemistry Vast majority of over 20 million known compounds are based on : organic compounds. Generally contain, + other elements Great variety of compounds Two Major oncepts NMENLATURE - Naming the molecules correctly and knowing the general classes of organic compounds REATIVITY - Studying patterns of reactivity within classes of compounds We will focus primarily on nomenclature but also show examples of reactivity Nomenclature Need to know Alkyl Groups - methyl = 3 ethyl = 3 2 propyl = butyl = Also pentyl, hexyl, heptyl, octyl, etc. R is "generic" alkyl group Alkyl groups may be combined with other elements or alkyl groups to give classes of compounds See the rganic hemistry Nomenclature Guide ALKANES Generic Alkane Representation: R- Generic Alkane Formula: n 2n+2 -yl +ane ALKANES Generic Alkane Representation: R- Generic Alkane Formula: n 2n+2 -yl +ane Ex: methane = 4 (methyl group + ) 3 - Ex: ethane = 3 3 (ethyl group + ) Page III-20-1 / hapter Twenty Lecture Notes

2 Page III-20-2 / hapter Twenty Lecture Notes ALKANES Generic Alkane Representation: R- Generic Alkane Formula: n 2n+2 -yl +ane Ex: propane = (propyl group + ) ALKANES Generic Alkane Representation: R- Generic Alkane Formula: n 2n+2 -yl +ane Ex: butane = (butyl group + ) Alkanes often called "saturated hydrocarbons" all carbons "saturated" with ALKANES - Isomers Isomers of Pentane But we can write butane in two ways: n-pentane 2-methylbutane n-butane 2-methylpropane These are isomers (same formula, structurally different). Name using "longest chain" alkane preceded by numbered alkyl groups 2,2-dimethylpropane 3-methylbutane would be incorrect - use smallest number possible Isomers of exane ow to Name a ompound Number of isomers grows as number of carbons increases Page III-20-2 / hapter Twenty Lecture Notes 1. Find the longest chain in the molecule. 2. Number the chain from the end nearest the first substituent encountered. 3. List the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached.

3 Page III-20-3 / hapter Twenty Lecture Notes ow to Name a ompound If there is more than one type of substituent in the molecule, list them alphabetically. YLALKANES ( n 2n ) +cyclo -yl +ane Ex: cyclohexane = 6 12 Generic ycloalkane Formula: n 2n (cyclohexyl group + ) Also cyclobutane, etc. Alkyl alides Generic Alkyl alide Representation: R-X X = halogen (F, l, Br or I) Ex: methyl iodide = 3 -I (methyl + iodide) also known as iodomethane ALLS Generic Alcohol Representation: R- -yl +anol Generic Alcohol Formula: n 2n+2 Ex: ethanol = 3 2 (ethyl group + ) Many other possibilities ALLS Generic Alcohol Representation: R- -yl +anol Generic Alcohol Formula: n 2n+2 Ex: 1-propanol = (propyl group + ) ALLS Generic Alcohol Representation: R- Note that both 1-propanol and 2-propanol exist 1-propanol Page III-20-3 / hapter Twenty Lecture Notes 2-propanol 3 -()- 3

4 Page III-20-4 / hapter Twenty Lecture Notes GLYLS Alcohols (diols) with Two Groups TYPES F ALLS Primary R 32, ethanol rubbing alcohol 3 R Secondary R 3 R R Tertiary Ethylene glycol (1,2ethanediol) Propylene glycol (1,2propanediol) R Glycerol (1,2,3-propanetriol) Alcohol with 3 Groups ETERS Generic Ether Representation: R--R Generic Ether Formula: n2n+2 Ex: diethyl ether = (ethyl + + ethyl) ETERS Two nomenclatures for ethers! KETNES Ethers also use "IUPA" Nomenclature Generic Ketone Representation: R--R (shorter alkyl group -yl +oxy) (longer group -yl +ane) R = alkyl group, = carbonyl (=) Generic Ketone Formula: n2n Two carbons connected to carbonyl Ex: 1-ethoxypropane = (ethyl -yl + oxy)(propyl -yl +ane) old school: ethyl 1-propyl ether Ex: propanone = 3-(=)-3 (methyl + = + methyl) 3 carbon atoms like propane Ex: 2-methoxypropane = 3(3)-3 2-(methyl -yl + oxy)(propyl -yl +ane) old school: methyl 2-propyl ether Also dimethyl ether, etc. Propanone is also known as Acetone Page III-20-4 / hapter Twenty Lecture Notes

5 Page III-20-5 / hapter Twenty Lecture Notes ALDEYDES Generic Aldehyde Representation: R-- R = alkyl group or, = carbonyl (=) Generic Aldehyde Formula: n 2n At least one connected to carbonyl Ex: methanal = 2 -= 1 carbon atom like methane Methanal is also known as Formaldehyde ALKYNES Generic Alkyne Representation: R- -R R = alkyl group or Generic Alkyne Formula: n 2n-2 Ex: 2-pentyne = carbon atoms like pentane Ethyne is also known as Acetylene ALKENES Generic Alkene Representation: R-=-R R = alkyl group or Generic Alkene Formula: n 2n Ex: trans-pent-2-ene = 3 -= carbon atoms like pentane cis (same side) trans (opposite) ALKENES - cis and trans cis-but-2-ene trans-but-2-ene Important! Differing reactivity in cis and trans isomers ALKENES - cis and trans is - trans isomerism occurs because the electronic structure of the carbon carbon double bond makes rotation energetically unfavorable. Page III-20-5 / hapter Twenty Lecture Notes Alkenes Many ccur Naturally

6 Page III-20-6 / hapter Twenty Lecture Notes ARMATI YDRARBNS Aromatic compounds use conjugated double bonds for increased stability. Flat, stable organic functional group ARMATI YDRARBNS Notice: aromatic compounds are flat rings with delocalized π electrons σ bonds σ and π bonds Simplest aromatic compound is Benzene, 6 6 π bonds ARMATI YDRARBNS More on The Ring Resonance in Benzene single bond: 154 pm = bond: 134 pm bonds in benzene: 139 pm bond order is π electrons delocalized 2 3 ARMATIS - Examples ARMATIS - Examples 3 ethylbenzene N 2 toluene phenol ortho position l l meta position l para position l nitrobenzene l l Br bromobenzene Naphthalene benzoic acid See andout 1,2-dichlorobenzene or o-dichlorobenzene Page III-20-6 / hapter Twenty Lecture Notes 1,3-dichlorobenzene or m-dichlorobenzene 1,4-dichlorobenzene or p-dichlorobenzene See andout

7 Page III-20-7 / hapter Twenty Lecture Notes ARBXYLI AIDS arboxylic Acids Generic arboxylic Acid Representation: R- Generic arboxylic Acid Formula: n 2n 2 Ex: propanoic acid = (propyl -2 + = + ) Acetic acid Benzoic acid Acids are found in many natural substances: bread, fruits, milk, wine arboxylic acid group with acidic + All are WEAK acids Formic acid = Vinegar is essentially acetic acid! arboxylic Acids AMINES Generic Amine Representation: R (3-x) -N x Ex: ethylamine = 3 2 -N 2 (ethyl + N 2 ) Formic acid, 2, gives the sting to ants. 3 Aspirin, acetylsalicylic acid Also diethylamine and triethylamine AMINES ESTERS Methylamine Dimethylamine Trimethylamine Amines generally have terrible odors! Generic Ester Representation: R 1 --R 2 Generic Ester Formula: n 2n 2 Ex: ethyl propanate = (propyl -2 + = + + ethyl) Similar to carboxylic acids adaverine Pyridine Page III-20-7 / hapter Twenty Lecture Notes Name R 2 first, then R 1

8 Page III-20-8 / hapter Twenty Lecture Notes AMIDES Generic Amide Representation: R x --N y R (2-y) Nomenclature and Models Ex: N-methylpropanamide 3 N N-groups off of nitrogen atom REATIVITY uge Topic, too vast for 222 We will look at a few general patterns of reactivity; Many more exist! Reactions of Alkenes: ADDITIN REATINS Alkenes are unsaturated more bonds can form to the atoms Molecules such as Br 2, 2, l, Br, and 2 add to the double bond + Br 2 Br Br 1,2-dibromoethane Br 2 2 Br- 2 Br REATIVITY Example #2: Addition Reactions Diatomics adding across double bond REATIVITY 2 = Example #1: Addition Reactions Diatomics adding across double bond Fats can be hydrogenated with 2. Many foods have hydrogenated fats Page III-20-8 / hapter Twenty Lecture Notes

9 Page III-20-9 / hapter Twenty Lecture Notes REATIVITY Example #3: Substitution Reactions Functional groups switch places REATIVITY Example #4: Elimination Reactions sp or sp 2 bond formation = N 3 Polymers Giant molecules made by joining many small molecules called monomers Average production is 150 kg per person annually in the U.S. (!) Polymers A Polymer literally means "many parts" Many mer (or monomer) units combined to make a polymer Polymers have high molar masses (10 7 g mol -1 or more!) and are used for plastic, fabric, Teflon, much more Synthesized by addition and condensation reactions * * n polyethylene REATIVITY Example #5: Addition Polymerization Reactions Polymers built from sp 2 carbons (pi bonds) Polyethylene Synthesis hain initiator: benzoyl peroxide eat. 2 Initiation Step: Reaction of benzoyl radical A polymer with a molar mass of 1e 6 has about 360,000 units Page III-20-9 / hapter Twenty Lecture Notes

10 Page III / hapter Twenty Lecture Notes Polyethylene Synthesis hain Propagation: Addition of further ethylene n n + 1 Types of Polyethylene Linear, high density PE (DPE) hain Termination: Reaction of two radicals n n Branched, low density PE, LDPE ross-linked PE, LPE Polystyrene REATIVITY Example #6: ondensation Polymerization Reactions ondensation reactions combine different functional groups to make polymers with different properties Polystyrene (PS) is a nonpolar material and dissolves in organic solvents. PS foam is mostly air, and when it dissolves it collapses to a much smaller volume. Very powerful reaction mechanism; used in contact lenses, nylon, much more REATIVITY Example #6: ondensation Polymerization Reactions n ondensation Polymers + n 2 2 terephthalic acid ethylene glycol Polyester Page III / hapter Twenty Lecture Notes 2 2 Polyethylene terephthalate (PET), a polyester n + 2

11 Page III / hapter Twenty Lecture Notes Polyesters (PET) Jackets made from recycled PET soda bottles REATIVITY Example #6: ondensation Polymerization Reactions Soda bottles, mylar film. Nylon-6,6 Polyamides: Nylon Each monomer has 6 atoms in its chain. A polyamide link forms on elimination of l Result = nylon-6,6 USES FR PLYMERS Examples of Polymers: Teflon - polytetrafluoroethylene Fabric - polyester, polyacrylonitrile Milk & soda bottles - (igh Density) Polyethylene Styrofoam - polystyrene plastic wrap (Saran) - poly(vinylidene chloride) contact lenses - poly(methyl methacrylate) ther uses: Bubble Gum! A copolymer Slime! Slime is polyvinylalcohol cross-linked with boric acid Styrene + butadiene Page III / hapter Twenty Lecture Notes

12 Page III / hapter Twenty Lecture Notes Polymer Recycling Symbols PETE = Polyethylene terephthalate, DPE = igh density PE, g/cm 3 V = PV (polyvinyl chloride), See: hapter Twenty Study Guide hapter Twenty oncept Guide End of hapter 20 LDPE = Low density PE, g/cm 3 PP = Polypropylene, g/cm 3 PS = Polystyrene, g/cm 3 ther = ther plastics (varies) Page III / hapter Twenty Lecture Notes