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General Chemistry I 1
BONDING INORGANIC MOLECULES
7.1 Petroleum Refining and the Hydrocarbons
7.2 The Alkanes
7.3 The Alkenes and Alkynes
7.4 Aromatic Hydrocarbons
7.5 Fullerenes
7.6 Functional Groups and Organic Reactions
7.7 Pesticides and Pharmaceuticals
7CHAPTER
General Chemistry I
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307
Organic Chemistry:the study of the compoundsof carbon
7.1 PETROLEUM REFINING AND
THE HYDROCARBONS
Hydrocarbons:compounds of carbon andhydrogen
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7.2 THE ALKANES309
Normal alkanes, n-alkanes
~ straight-chain (linear) alkanes, CnH2n+2
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Fig. 7.1. Bonding in alkanes involves sp3 hybridized orbitals.
Fig. 7.2. Rotation about C–C bond variable conformations
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‘staggered’ conformer ‘eclipsed’ conformer
(sp3-sp3)(sp3-s)(sp3-s)
Conformers (conformations) are isomers that can be interconverted via bond rotations. They are stereoisomers.
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310
Two conformations of C16H34
Londondispersion
force
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Fig. 7.5. Fractional distillation of petroleum.
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Cyclic Alkanes: Carbon atoms arranged in rings
Cyclopropane, C3H6 Cyclobutane, C4H8 Cyclohexane, C6H12
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- cycloalkanes have one ring: CnH2n
- angle strain energy reducing the stability of small rings (< C5) CCC bond angle smaller than the sp3 tetrahedral angle of 109.5o
angle strainedunstrained
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Fig. 7.7. Conformations of cyclohexane. (a) Chair. (b) Boat.
Cyclohexane, C6H12
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C
CC
C
CC
H2C
H2CCH2
CH2
CH2
H2C
or or
H HH
H
H H
HH
HHH
H
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Branched-Chain Alkanes and Isomerism
Fig. 7.8. Two isomeric hydrocarbons with the molecular formula C4H10.(a) Butane. (b) 2-Methylpropane (branched chain isomer).
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-Branched chain hydrocarbons contain only C-C and C-H single bonds, but not in a straight chain. They are constitutional(structural) isomers of normal alkanes. Isomers are different structures with the same molecular formula.
Constitutional isomers have different atomic connectivities: they can be interconverted only by bond-breaking and bond-making processes.
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ISOMERS
CONSTITUTIONALISOMERS
STEREOISOMERS
Branch isomersPosition isomersFunctional groupisomers
Geometric isomersOptical isomersConformers
Differ in atomicconnectivity
Have same atomicconnectivity, butdiffer in spatialarrangement ofatoms
Slide 17
Slide 18
Slides 4 & 8
Slide 9
Slide 18
Slide 33
Interconversion of all isomers, except conformers, requiresbond breaking and remaking
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Nomenclature for isomeric alkanes (IUPAC: International Union of Pure and Applied Chemistry)
1. Find the longest (backbone) alkane chain (= root, named
according to slide 3)
2. Alkyl groups (branches)
Methyl –CH3 Ethyl –CH2CH3
Propyl –CH2CH2CH3 Isopropyl –CH(CH3)2
3. Numbering of carbon atoms
(lowest number for the attached position)
4. Prefixes for many alkyl groups
di-, tri-, tetra- , penta-
5. Alphabetical order for different alkyl groups
(E.g. ethyl before methyl before propyl)
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EXAMPLE 7.1
Name the following branched-chain alkane:
1 3 4 5 62
4-ethyl-2,4-dimethylhexane
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Octane number
Straight-chain alkanes burn very unevenly “knocking”
Heptane (octane number, 0) Isooctane (octane number, 100)
Octane number, 90 90% (by vol) isooctane + 10% heptane
Anti-knocking additive: tetraethyllead, Pb(C2H5)4 (now banned!)
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7.3 THE ALKENES AND ALKYNES314
Unsaturated hydrocarbons
Alkene ~ double bonds E.g. Ethene (Ethylene), C2H4
Alkyne ~ triple bonds E.g. Ethyne (Acetylene), C2H2
Fig. 7.10. Reaction with KMnO4.(a) No reaction with hexane.(b) Redox reaction with 1-hexene. Products: MnO2 and CH3(CH2)3CH(OH)CH2OH
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Ethylene, H2C=CH2
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Acetylene, HC≡CH315
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Optical isomerism and chirality
Fig. 7.9. Non-superimposable optical isomers of a molecule CHBrClF.
Optical isomers:
Non-superimposable mirror image structures are called
enantiomers
Same physical properties but with different optical activity
Chemical properties can differ when they interact with other
optically active molecules → Pharmaceutically important! Optical activity:
Rotating the plane polarized light clockwise or anti-clockwise
Chirality (handedness) ~ C*: chiral center
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Position isomers of alkenes and alkynes
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C4H8: CH2=CH-CH2-CH3 CH3-CH=CH-CH3
C4H6: HCC–CH2–CH3 H3C–CC–CH3
1-butyne 2-butyne
1-butene 2-butene
Geometric isomers of alkenesE.g. 2-butene
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Fig. 7.14. Configurational change of the trans isomer of 2-butene to its cis isomer upon absorbing UV light. * transition.
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Fig. 7.13. The overlap between the two p orbitals decreases when the2-butene molecule is twisted about the C=C bond.
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Polyenes
1,3-butadiene, CH2=CH–CH=CH2
Fig. 7.15. The four MOs formed from four 2pz AOs in 1,3-butadiene. Only the twolowest orbitals are occupied in the ground state.
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conjugated electron
system
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7.4 AROMATIC HYDROCARBONS319
Benzene, C6H6
Fig. 7.16. The six molecular orbitals for benzene.
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BTX (benzene-toluene-xylene)
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- hydrodealkylation: from toluene to benzene, 550-650 oC, 40-80 atm
(1,2; 1,3; 1,4-dimethylbenzenes)(methylbenzene)
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Reforming reactions: producing BTX aromatics from straight chain alkanes
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7.5 FULLERENES322
- Buckminsterfullerene: the third allotrope of carbon
- a whole family of closed-cage carbon molecules
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“for their discovery of fullerenes”
Robert F. Curl, Jr. Harold W. Kroto Richard E. Smalley
The Nobel Prize in Chemistry 1996323
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Carbon nanotubes : one of the purest carbon forms
• Single-walled nanotubes (SWNTs)
- a single graphite sheets wrapped into a cylindrical tube
• Multi-walled nanotubes (MWNTs)
- an array of concentrically nested nanotubes
Baughman, R. H. et al. Science 2002, 297, 787
Carbon Nanotubes (CNTs)323
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Graphene-Based Materials
D. Li et al. Science 2008, 320, 1170
• graphenes – monolayers of carbon atoms arranged in a honeycomb network
• simply prepared by pulling an atomic layer off of a graphite crystal with a piece of sticky tape
• a giant aromatic macromolecule that conducts both electricity and heat well in two dimensions
• high specific surface area, high mechanical strength comparable to CNTs
• production cost lower than that of CNTs
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7.6 FUNCTIONAL GROUPS AND ORGANIC REACTIONS
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Halides R–X (X = F, Cl, Br, I) Halo-
Free radical chain reaction
Cl2 → 2 Cl ∙ (initiation)
Cl ∙ + CH4 → HCl + ∙ CH3 (propagation)
∙ CH3 + Cl2 → CH3Cl + Cl ∙ (propagation)
CH4 + Cl2 CH3Cl + HClo250 400 C, h
Addition and elimination reactions
ClCH2CH2Cl CH2=CHCl + HClo500 C, charcoal
CH2=CH2 + Cl2 → ClCH2CH2Cl
vinyl chloride (chloroethene)monomer of PVC
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chloromethane
+ other products
1,2-dichloroethane
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Alcohols R–OH – OH group -ol, hydroxy-
Methanol (methyl alcohol), CH3OH
CH4(g) + H2O(g) → CO(g) + 3 H2(g) (reforming reaction) CO(g) + 2 H2(g) → CH3OH synthesis gas
Ethanol (ethyl alcohol), C2H5OH
CH2=CH2 + H2O → CH3CH2OH
CH3CH2CH2OH: 1-propanol (propyl alcohol)
CH3CH(OH)CH3: 2-propanol (isopropyl alcohol)
CH3CH(OH)CH2CH3: 2-butanol or 2-hydroxybutane
2H O 4HSO
+H
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Position isomers
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Types of Alcohols
Primary alcohol: RCH2–OH
ethanol
Secondary alcohol: R2CH–OH
2-butanol
Tertiary alcohol: R3C–OH 2-methyl-2-propanol tertiary-butyl alcohol or tert-butanol (CH3)3COH
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Phenols C6H5OH or Carbolic acid Weak acid, but stronger than EtOH
Partial oxidation of benzene, distillation of coal
Toxic: lethal dosage, 1g
Major Synthetic Process (the cumene process)
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Ethers R–O–R’ –O– group
CH3CH2–O–CH2CH3, diethyl
ether
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- methyl t-butyl ether (MTBE)
- cyclic ethers: epoxides
E.g. epoxyethane (ethylene oxide)
Alcohols and ethers of same molecular formula arefunctional group isomersE.g. ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3), both C2H6O
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Aldehydes
“Formalin” : aqueous solution of HCHO preservation of biological specimens
‘Sick house syndrome’
-CHO group –al
▶ HCHO, methanal (formaldehyde)
▶ CH3CHO, ethanal (acetaldehyde)
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Fig. 7.23. Bonding in formaldehydeinvolves sp2 hybrid orbitals of bothC and O.
(H)RC
O
H
C O
H
H
(sp2-sp2)(sp2-1s) sp2
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Ketones –one
(CH3)2CO, propanone (acetone)
Good solvent, miscible with water
Oxidation of secondary alcohol:
CH3CH2CH2COCH3, 2-pentanone
CH3CH2COCH2CH3, 3-pentanone
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>CO group
RC
O
R'
Position isomers
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Carboxylic Acids R–COOH –oic acid
▶ Carboxyl group:
HCOOH, methanoic acid (formic acid)
CH3COOH, ethanoic acid (acetic acid)
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C
O
OH
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Esters
Product of the reaction between a carboxylic acid and an alcohol
Ethyl ethanoate (ethyl acetate)
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Fragrant odors, flavors of fruits
–oate
R
C
O
OR'
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★ Fats
Hydrogenation of oils (esters of cis-unsaturated fatty
acids)
Saturated fats with higher m.p.:
→ solid, good for baking and extended shelf-life
Remaining double bonds converted from
cis to trans isomers → bad for health!
+ 6H2 → saturated fats
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Triglyceride ester
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Amines334
Primary amine: RNH2
Secondary amine: R2NH Tertiary amine: R3N
Condensation product of an amine with a carboxylic acid
◆ Amides: R–(CO)–(NH)–R’ -CONH- group -amide (or amido-)
an amide
>N- group –amine (or amino-)N
R'(H)
(H)R'' R Weak bases
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Amino acids, NH2–R–COOH ~ bifunctional molecules
Glycine, NH2CH2COOH
α-amino acid, +H3NCH2CO2– (pH = 7)
Peptide
~ Condensation product of two or more amino acids Peptide bonds –(CO)–(NH)– (amide bonds)
Functional Groups in Proteins332
‘zwitterion’
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Protein ~ Polypeptide
primary, secondary, tertiary, quaternary structures
tertiary structure of theenzyme chymotrypsin
binding of phenylalanine in the active site of chymotrypsin
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expanded view of theactive site of chymotrypsin
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7.7 PESTICIDES AND PHARMACEUTICALS
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Insecticides ( 살충제 )
First-generation
Copper, Lead, Arsenic, Nicotine → aphid
Second-generation
DDT (dichlorodiphenyltrichloroethane):→lice
Methyl parathion
Third-generation
Target oriented, environmentally degradable
E.g. sex attractant, Juvenile hormone ~
Methoprene
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Herbicides ( 제초제 )
2,4-D (2,4-dichlorophenoxyacetic acid) 2,4,5-T (“Agent Orange,” or 2,4,5-trichlorophenoxyacetic
acid) → Defoliant used during Vietnam war
→ Contains trace amount (10 ppb) of TCDD
TCDD (“dioxin,” or 2,3,7,8-tetrachlorodibenzo-p-dioxin)
Extremely toxic ! Waste-burning incinerator
→ major source of dioxin in the environment
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Analgesics ( 진통제 )
Aspirin (acetylsalicylic acid)
Analgesic (pain reliever), Antipyretic (reduces fever),
Prevents heart disease (thins the blood)
Carboxylic acid Irritates stomach
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Acetaminophen (4-acetaminophenol)
“Tylenol” ~ weakly acidic phenol
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Much more powerful pain relievers
Morphine ~ natural product from “opium poppy” Codeine ~ also cough suppressant and analgesic Heroin ~ 3,6-diacetylmorphine
2~3 times powerful than morphine and more addictive
Morphine Codeine Heroin
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A Little Joke on Nomenclature
A research chemist walked into a pharmacy and asks, “Do you have (5,6)-7,8-didehydro-4,5-epoxy-3-methoxy-17-methylmorphinan-6-ol?”The pharmacist scratched her head and said, “Do you mean codeine?”“That’s it!”, said the chemist, “I can never remember that word!”
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Antibacterial Agents (Antibiotics) Sulfanilamide
Bacteria mistake sulfanilamide for p-aminobenzoic acid
→ Interferes with bacteria’s synthesis of folic acid, Penicillin ~ natural product formed by certain molds
~ Total synthesis by John C. Sheehan (1957)
~ Fermentation (more economic)
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“Steroid nucleus” 3 six-atom rings and 1 five-atom ring
Cholesterol ~ synthesized in the liver from acetate units
via the ‘mevalonate pathway’. It is the biological precursor
to most other steroids
Cortisone ~ secreted from adrenal glands
~ controls metabolism of sugars, fats, and proteins
Progesterone, Estrogen
~ Female sex hormones, oral contraceptives
Testosterone ~ male sex hormone
Steroids: derived from cholesterol
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10 Problem Sets
For Chapter 7,
4, 12, 20, 28, 30, 32, 40, 44, 46, 50