CHEM 232 University of Illinois Organic Chemistry I at Chicago UIC

Organic Chemistry 1 Lecture 3

Instructor: Prof. Duncan Wardrop Time/Day: T & R, 12:30-1:45 p.m. January 19, 2010

1 Lecture Summary

Revision & Proof of Resonance Introduction to Hydrocarbons Classi!cation Structure & Bonding Nomenclature

University of Slide 2 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 2 Revision of Resonance

Do not confuse equilibrium with resonance: double-headed arrows represent resonance contributors; two separate arrows represent the equilibrium of distinct chemical species....

O O

Resonance (electrons move) MeO MeO

H O O H H H Equilibrium (atoms move)

University of Slide 3 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 3 The first pair of structures are descriptions of the same - the overall description is based on a weighted combination of the two extremes. The second pair of structures are distinct : one is a and the other an enol. For more details about this chemical transformation, see Chapter 18. Prioritizing Resonance Contributors (How much Unicorn?!) Priority 1 No !rst-row elements (B, C, N, O) can have more than eight electrons in its valence shell.....

O O O N N N O O O

Equal Equal Non-Permissable Contributor Contributor Contributor (N has 10 elect.)

University of Slide 4 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 4 Prioritizing Resonance Contributors

Priority 2 Resonance structures in which all atoms are surrounded by an octet of electrons are almost always lower in energy than those resonance structures in which one or more atoms are electron de!cient.

8 electrons 8 electrons H H H O O O C-O Bond Length 120 pm (C=O) 6 electrons 128 pm (calculated) 143 pm (C-O)

More Stable

University of Slide 5 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 5 Prioritizing Resonance Contributors

Priority 3 Resonance structures with charge separation are typically higher in energy than those without. If charge separation exists, then electropositive atoms (C, B) are better able to bear +ve charge... Small Dipole Moment Major Unimportant Physical Contributor Contributor Evidence

H H H H

H H 0.66 D

University of Slide 6 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 6 Prioritizing Resonance Contributors

Priority 4 If charge separation exists in a resonance structure, then the electronegative atoms should gain the formal negative charge and vice versa:

O O O

Unimportant Major Minor Contributor Contributor (but significant) 4.02 D Contributor

University of Slide 7 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 7 Self Test Question

Rank the following acids in order of increasing acidity. a.

O + H OH O d. O + H O b. O SH S + H OH O A. a, c, b, e, d H N e. N + H B. e, c, a, b, d c. C. c, e, a, d, b OH O + H D. b, a, c, d, e E. d, b, a, c, e

University of Slide 8 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 8 There are a number of structural features which effect the pKa of an acid: a) Electronegativity; b) The strength of the bond to the acidic hydrogen atom; c) Inductive effects; d) Resonance delocalization in conjugate base. Self Text Question

Which is the most acidic proton in the molecule below?

e A. a H H O O a B. b H H O d C. c H H H O H b D. d H c E. e

University of Slide 9 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 9 Free Organic Chemistry Tutoring in the SLC

Where: Science & Learning Center (201 SES)

Who: Dr. Bob Widing

When: Tuesday & Thursday, 1-5 p.m. Monday & Wednesday afternoons

Look for a molecular model set and you’ll know you’ve found the right person. If he’s in the SLC, Dr. Widing is willing to help.

University of Slide 10 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 10 Quiz This Week

This will be the last notice about quizzes. You should expect a quiz in your discussion section every week.

• Quiz this week during your discussion section • Topic = Chapter 1 • Only top ten quiz scores (25 points each) count • No makeup quizzes; minimum 12 quizzes

University of Slide 11 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 11 Molecular Model Set

• A molecular model set is highly recommended • Essential for Chapters 3 & 7 • Any set is !ne; your preference; available in bookstore • Bring your set to class and discussion section

University of Slide 12 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 12 CHEM 232 University of Illinois Organic Chemistry I at Chicago UIC Classes, Bonding & Structural Features of Hydrocarbons

Sections 2.1, 2.5-2.10

13 Classes of Hydrocarbons

Hydrocarbons • only C & H atoms • framework for funct. groups Aliphatic • generally, non-reactive Aromatic • aka: arenes • many isolated from plants; • aleiphar Greek for “fat” impurities can be fragrant • sources were fats and oils • aromaticity de!niton: Ch. 12

Alkanes Alkenes

• only single bonds • contain a double bond • contain a triple bond • nomenclature: -ane suffix • nomenclature: -ene suffix • nomenclature: -yne suffix

University of Slide 14 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 14 Examples of Aliphatic Hydrocarbons butane 1-butene 1-butyne

H H H H H H H H H H C C C C H H C C C C H C C C C H H H H H H H H H H H

CH CH CCH CH3CH2CH2CH3 CH3CH2CHCH2 3 2

Alkanes Alkenes Alkynes • only single bonds • contain a double bond • contain a triple bond • CnH2n+2 • CnH2n (1 double bond) • CnH2n-2 (1 triple bond) • nomenclature: -ane • nomenclature: -ene • nomenclature: -yne suffix suffix suffix

University of Slide 15 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 15 Examples of Aromatic Hydrocarbons

Aromatic • aka: arenes H • many isolated from plants; H C H C C impurities were fragrant C C • aromaticity de!niton: Ch. 12 H C H H • many are derivatives of benzene benzene benzene • resonance: delocalized electrons CH3 N • adjacent double bonds O • planar (120º bond angles) • polyaromatic hydrocarbons toluene napthalene pyridine furan (PAHs) contain two or more aromatic rings; highly carcinogenic and environmental toxin

University of Slide 16 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 16 Structural Features of Simple Alkanes

• 4 bonds to carbon, 1 bond to H • C–H bond length ~ 110 pm • C–C bond length ~ 153 pm • all bond angles are nearly tetrahedral

University of Slide 17 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 17 Initial Valence Bond Model of Carbon

H H 1s 1s H H C C 2p 2p 2p 2s • carbon only has two half-!lled orbitals • should, then, form two bonds • actually forms 4 bonds!?!?

University of Slide 18 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 18 Valence Bond Model: Hybridization

2p 2p 2p mix s & p orbitals

2s sp3 sp3 sp3 sp3 • hybrids: mixture of s & p; sp3 lower in energy than p • 25% s-character and 75% p-character • 4 degenerate orbitals = equal in energy • each half-!lled, can form 4 bonds • VSEPR: tetrahedral (bond angles = 109.5º) University of Slide 19 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 19 Understanding the Shape of sp3 Orbitals

constructive + interference + + – + –

destructive + – interference x3

• constructive interference: reinforce electron wave where sign is the same • destructive interference: cancel out wave where sign is opposite • higher probability of !nding an electron on one side of the nucleus

University of Slide 20 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 20 Sigma Bonds (σ-bond) in Methane

= group is pointing toward you, in front of the plane of paper H C(2sp3)––H(1s) = group is pointing away σ-bond from you, behind the plane H of paper C H = group is either toward or away from you, usually denotes mixtures 109.5º H = group lies in the plane of the drawing surface • σ-bond: head-to-head overlap of orbitals; strongest bond type • hybridization increases bond strength of σ-bonds since electrons are concentrated on one side of nucleus • only larger lobe of sp3 involved in bonding • typically ignore (don’t draw) smaller lobe

University of Slide 21 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 21 The C–C σ-bond in Ethane

• in-phase overlap of an sp3-hybridized orbital from each carbon atom • overlap is along internuclear axis (σ-bond) • VSEPR: tetrahedral around each carbon atom

University of Slide 22 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 22 CHEM 232 University of Illinois Organic Chemistry I at Chicago UIC

Nomenclature of Hydrocarbons

Sections: 2.11-2.15

23 What’s In a Name?

IUPAC: sodium dodecyl sulfate Common: sodium lauryl sulfate Trade: SDS

IUPAC: ethyl (3R,4R,5S)-5-amino-4-acetamido-3- Cl (pentan-3-yloxy)cyclohex-1-ene-1-carboxylate Generic: oseltamivir HO Trade: Tamiflu O HO Cl O O OH O N CH3 IUPAC: Sodium (2S)-2-amino-5- HO hydroxy-5-oxo-pentanoate OH Common: mono sodium glutamate Cl H C CH : 1,6-Dichloro-1,6- 3 3 Initialism: MSG IUPAC dideoxy-β-D-fructofuranosyl-4- chloro-4-deoxy-α-D- IUPAC: N,N-diethyltoluamide galactopyranoside Initialism: DEET Common: sucralose Trade: OFF Trade: Splenda

University of Slide 24 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 24 IUPAC: Alkanes with NO IUPAC: International Union of Pure and Applied Chemistry

common name retained

Greek prefixes

University of Slide 25 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 25 Constitutional (Structural) Isomers

constitutional isomers: same molecular formula; different connectivity connectivity: order in which the atoms are bonded

C9H20 C9H20 Identical

C9H20 C9H20

University of Slide 26 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 26 Common Names for Branched Isomers of Simple Alkanes homologous series: n-butane n-pentane n-hexane succesive members differ by a –CH2– group iso-butane iso-pentane iso-hexane

methyl: CH3

methylene: CH2 neo-pentane neo-hexane

methine: CH n iso neo CH3 CH “normal” 3 CH C straight chain H C 3 H3C CH3

University of Slide 27 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 27 Common Names Become Too Complex: Systematic Method of Naming is Needed

University of Slide 28 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 28 IUPAC: Naming Alkyl Groups

substituent: atom or group other than H bonded to carbon alkyl group: one H atom less than an alkane

H H H H C C CH CH3CH2CHCH2CH2CH3 H C C C 3 3 CH H3C H H H 3

Steps: 1. Identify longest continuous chain of carbon atoms. 2. Locate substituents attached to the longest continuous chain of carbon atoms. 3. Name alkane substituent by replacing -ane of parent alkane with -yl

CH3CH3 CH3(CH2)5CH3 CH3(CH2)16CH3 Ethane Heptane Octadecane

University of Slide 29 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 29 Common & IUPAC Names of 3-Carbon Alkyl Groups

University of Slide 30 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 30 Common & IUPAC Names of 4-Carbon Alkyl Groups

University of Slide 31 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 31 Carbon Classi"cation

University of Slide 32 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 32 IUPAC: Alkanes with One substituent (Monosubstituted) 2 4 6 3 CH3CH2CHCH2CH2CH3 1 5 CH3 3-methylhexane Steps: 1. Identify the longest continuous chain of carbons. 2. Identify substituent group (group not part of the longest continuous chain). 3. Number the longest chain so that substituent has the lowest number. 4. Name the compound according to the figure below.

Conventions: • locant refers to the numerical location of a substituent • numbers and letters are always separated by a dash (-)

substituent parent alkane locant name name

University of Slide 33 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 33 IUPAC: Alkanes with Two or More Different Substituents

CH3 CH2CH3 2 4 6 CH3CHCH2CHCH2CH2CH3 1 3 5 7 4-ethyl-2-methylheptane Steps: 1. Identify the longest continuous chain of carbons. 2. Identify substituent groups (groups not part of the longest continuous chain). 3. Number the longest chain so that substituents have the lowest locants. 4. Name the compound according to the figure below. Conventions: • if two numbering give same parent, number chain to maximize number of substituent groups. • order the substituents in the name alphabetically • Follow First Point of Difference Rule: Number the chain so that the locant at the first point of difference has the lowest value (e.g. 2,2,4 better than 4,2,2) if two numberings give same locants, choose numbering that gives lower locant to first in alphabet substituent name substituent name locant locant parent alkane first in alphabet 2nd in alphabet

University of Slide 34 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 34 IUPAC: First Point of Difference Rule

Number the chain (or ring) so that the locant at the first point of difference in the name has the lowest value The correct set of locants is NOT the one with the lowest sum!

Correct Name 1 3 5 7 4-ethyl-2-methylheptane 2 4 6

first point of difference

7 5 3 1 4-ethyl-6-methylheptane 6 4 2

University of Slide 35 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 35 Self Test Question

What is the IUPAC name for the molecule below?

A. 2-methyl-4-propylheptane 1 3 5 7 2 4 6 B. 4-propyl-6-methylhexane C. 2-methyl-4-butylhexane D. 2,4-methylethylheptane E. 4-propyl-2-methylheptane

University of Slide 36 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 36 IUPAC: Alkanes with Repeating Substituents

CH3 CH3 CH CCH CHCH 2 4 3 2 3 1 3 5 CH3 2,2,4-trimethylpentane Steps: 1. Identify and number the longest continuous chain of carbons to provide lowest values of locants. 2. Identify substituent groups (groups not part of the longest continuous chain). 3. Use replicating prefixes ( e.g. di, tri, tetra) to indicate total number of substituents on parent 4. Name the compound according to the figure below. Conventions: • List each locant separately. Separate numbers with a comman, no space. • Prefixes are not considered when alphabetizing substituent names. • Follow First Point of Difference Rule: Number the chain so that the locant at the first point of difference has the lowest value (e.g. 2,2,4 better than 4,2,2) replicating locant locant substituent parent alkane , prefix University of Slide 37 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 37 IUPAC: First Point of Difference Rule

Number the chain (or ring) so that the locant at the first point of difference in the name has the lowest value The correct set of locants is NOT the one with the lowest sum!

1 3 5 7 2 4 6 8 2,3,3,7,7-Pentamethyloctane

first point of difference

8 6 4 2 7 5 3 1 2,2,6,6,7-Pentamethyloctane Correct Name

University of Slide 38 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 38 IUPAC: Alkanes with Branched Substituents (Using Common Substituent Names)

CH3 H C CH 3 C 3 3 4 6 8 5 7 9 CH3CH2CHCH2CH2CHCH2CH2CH3 2 1 H3C CH2CH3 2-methyl-3-ethyl-6-tert-butylnonane

Steps: 1. Identify and number the longest continuous chain of carbons to provide lowest values of locants. 2. Identify common substituent groups (isopropyl, sec-butyl, isobutyl, tert-butyl). 3. Name the compound according to the figure below. Conventions: • List each locant separately. Separate numbers with a comman, no spaces. • Prefixes are not considered when alphabetizing substituent names. • Always follow first point of difference rule. • Neo-pentyl is not used as a common substituent name

common locant parent alkane substituent

University of Slide 39 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 39 IUPAC: Alkanes with Branched Substituents (Using IUPAC Substituent Names) 3 5 2 4 6 8 CH3CH2CH2CH2CHCH2CH2CH2CH3 7 9 1 CH3 1 2 3 CH2CCH3 CH3 5-(2,2-dimethylpropyl)-nonane

Steps: 1. Identify and number the longest continuous chain of carbons to provide lowest values of locants. 2. Identify and number longest chain is substituent group beginning with point of attachment to parent. 3. Name the compound according to the figure below. Conventions: • Follow all other steps and conventions for both chains. • Substituent name is placed within parentheses when preceded by locants of its own. • Parentheses are separated from outside words by a dash, no spaces.

parent 2nd chain substituent 2nd chain name parent chain name locant ( locant )

University of Slide 40 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 40 Self Test Question

What is the IUPAC name for the molecule below?

A. 5-(1-methylpropyl)-2,2- dimethyloctane 1 3 5 B. 2,2-dimethyl-5-sec-butyloctane 2 4 C. 4-sec-butyl-7-tert-butyloctane 6 8 7 D. 2,2,6-trimethyl-5-propyloctane E. 2-methyl-5-butyloctane

University of Slide 41 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 41 IUPAC: Monosubstituted Cycloalkanes

4 H2 C H 3 H2C C 1 C CH2CH2CH3 2 H2 propylcyclobutane

Steps: 1. Count the number of carbons in the ring. Precede the parent name with cyclo. 2. Identify straight chain, common or branched substituent groups. 3. Name the compound according to the !gure below. Conventions: • If the number of carbons in the substituent is greater, name the ring as the substituent as a cycloaklyl substituent (e.g. cyclobutyl) • If the ring is monosubstituted, no locant is neccessary; substituent locant is assumed to be 1.

substituent “cyclo” parent ring name

University of Slide 42 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 42 IUPAC: Disubstituted Cycloalkanes

H3CH2C H CH C HH H2 3 2 C 2 3 H C C C 9 1 1 2 4 4 CH CH2 CH3 H2C C C 8 6 C H2C CH 5 2 3 HHH2 7 H2 CH3 1,1-diethyl-4-(3-methylbutyl)cyclononane

Steps: 1. Count the number of carbons in the ring. Precede the parent name with cyclo. 2. Identify straight chain, common or branched substituent groups. 3. Name the compound according to the !gure below. Conventions: • If the number of carbons in the substituent is greater, name the ring as the substituent as a cycloaklyl substituent (e.g. cyclobutyl). Follow all previous steps and conventions for naming substituents. • List substituents in alphabetical order. Ignore replicating pre!xes. • Follow !rst point of difference rule.

substituent 1st substituent 2nd “cyclo” parent ring locant locant alphabetically alphabetically name

University of Slide 43 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 43 Self Test Question

What is the IUPAC name for the molecule below? A. 1-ethyl-3-pentylcyclohexane B. 3-ethyl-1-pentylcyclohexane C. 1-ethyl-3-(3-methylbutyl)cyclohexane D. 1-butyl-3-ethylcycloheptane 6 1 2 E. 1-(2-methylbutyl)-3-ethylcyclohexane 5 3 1 2 3 4 4

University of Slide 44 CHEM 232, Spring 2010 Illinois at Chicago UIC Lecture 3: January 19 44 CHEM 232 University of Illinois Organic Chemistry I at Chicago UIC

Next Lecture. . .

Chapter 2, Sections: 2.16-2.22 Chapter 3, Sections: 3.1-3.3

45