Chem. 1B – 12/3 Lecture. Announcements I Lab Final –On Wed./Thurs. Next Week –Will be 25 questions, multiple choice –Bring green type scantron (sorry,

Chem. 1B – 12/3 Lecture

Announcements I

• Lab Final– On Wed./Thurs. Next Week– Will be 25 questions, multiple choice– Bring green type scantron (sorry, don’t

have # yet)– Questions will be similar to quiz questions,

pre-lab questions, and post-lab questions

• Make Up Quiz– First 10 to 15 min. on December 8th

– Optional, will replace lowest quiz score (if higher)

Announcements II

• Class Grading– Blackboard score – I’m getting lab

instructors to report zeros in place of no score, so this will cause some Blackboard scores to go down to their actual scores

• Today’s Lecture– Organic Chemistry (Chapter 20)

• Carbon – carbon bonds• Alkanes• Alkenes

Chapter 20 Organic Chemistry

• Introduction– Organic Chemistry is a major area of

study (we offer 7 organic chemistry classes at the undergraduate level)

– In ~1 week, we only have time to introduce basic principles of organic chemistry


• Overview– Nature of Carbon – Carbon Bonds– Hydrocarbons (structure, naming and

isomers)– Reactions– Aromatic Hydrocarbons– Functional Groups


• Nature of Carbon – Carbon Bonds– Carbon is one of the few elements that form

fairly stable bonds with itself– Most alkanes (hydrocarbons with only single

bonds), while combustible in air (more stable as CO2 + H2O), have negative Gfº

– Carbon “likes to” form 4 bonds ([He]2s22p2, but mostly forms sp to sp3 hybrid bonds)


• Nature of Carbon – Carbon Bonds– Simplest hydrocarbon is CH4, methane,

in which sp3 hybridization occurs (tetrahedral geometry)

– As carbon – carbon bonds are common, in alkanes, they also occur with sp3 hybridization (tetrahedral for each C atom)

H


• Nature of Carbon – Carbon Bonds– Example alkane with a carbon – carbon

bond is ethane: CH3CH3

– All bonds are sigma bonds in alkanes– This means constituents may rotate

about bond

C

H

H

C

H

H

HH

C

H

HCH

H

H


• Nature of Carbon – Carbon Bonds– Hydrocarbons containing double bonds

are known as alkenes– Hybridization is sp2 (see ethene structure

below – drawn in 3D) so all atoms in one plane

CH

H

C

H

remaining p orbital forms bond

Because of bond, rotation about C-C axis doesn’t occur at room temperature

H


• Hydrocarbon Structures– Linear alkanes:

CH3(CH2)nCH3

– Carbon skeleton structure– Example butane =

– Only bonds shown as lines and carbons as kinks (Hs omitted)

No. Carbons

name

1 Methane

2 Ethane

3 Propane

4 n-Butane

5 n-Pentane


• Hydrocarbon Structures– Branched structures:

– Example isobutane = CH3CHCH3

CH3

– Butane and isobutane are “structural isomers” (have the same number of Cs and Hs, but are structurally different)

– Branched compounds have greater volatility than their linear isomers


• Hydrocarbon Structures– Optical Isomers

• As was mentioned in Chapter 24, tetrahedral structures with 4 different constituents (CWXYZ with C in center) will have optical isomers

• Hydrocarbon example (3-methyl hexane)

• “Chiral” carbon (carbon with 4 different constituents) shown with star


• Hydrocarbon Structures– Optical Isomers – cont.

• Two different (3D) structures can be drawn of 3-methyl hexane corresponding to mirror images

• Each “enantiomer” (version) will have identical properties except for ability to rotate light and ability to interact with other chiral compounds

• Reactions in living organisms typically produce only one of two mirror images (also known as enantiomers), while synthetic reactions often produce both isomers (known as racemic mixtures)


• Alkanes– Sources:

• Plant/animal products (mostly historic)• Petroleum (main source)• Synthesis from coal, natural gas, or biomass

– Structures:• Linear• Branched• Cyclic

Cyclopentane in C skeleton structure

Note: cyclopentane (C5H10) is NOT an isomer of n-pentane or isopentane (C5H12) as it has 2 fewer Hs


• Example of Contract for Alkane Research with Sacramento Based Alternative Fuel Company

• Company (Greyrock Energy) is working to produce diesel fuel from agricultural waste or “stranded” gas (natural gas normally vented in oil operations)

• They produce diesel in the following process:CnH2nOn + heat CO(g) + H2(g) and

CO(g) + H2(g) + catalyst H2n+2Cn (various) + H2O(l)


• Contract Research Example• My job (or that of students working for me) was to

determine H2n+2Cn (various) + other impurities (benzene, alkenes, alcohols)

• Four phases produced (liquid water, gas alkanes – methane to butane – used to generate power, hydrocarbon liquid or crude synthetic diesel, and wax or solid hydrocarbons)

• Q. Does structure of hydrocarbons matter?• A. Yes. Linear alkanes generally best for diesel,

while branched alkanes are good for gasoline but poor for diesel (increases octane rating)


• How did we determine the composition of the diesel fuel?Gas chromatography (similar to paper chromatography lab)

min0 5 10 15 20 25

pA

20

40

60

80

100

120

140

160

180

FID1 B, (YVONNE\08081301.D)

1.63

4 1.

707

1.75

6 1.

824

1.96

1 2.

040

2.08

7 2.

143

2.19

4 2.

267 2.

737

2.76

8 2.

809 2

.884 2

.974

3.12

0 3.

184

3.24

4 3.

317 3.

369

3.50

4

4.37

8 4.

407

4.51

9 4.

594

4.64

3 4.

784

4.85

8 5.

013

5.14

2 5.

289

5.65

8 6.

008

6.16

2 6.

292

6.42

3 6.

537

6.62

6 6.

706

6.76

4 6.

865

6.99

4 7.

164

7.63

2 7.7

23 7.

760

7.85

9 7.

940

8.06

9 8.

151

8.26

9 8.

349

8.46

8 8.

662

8.96

9 9.03

9 9.

078

9.12

5 9.

209

9.26

2 9.

472

9.57

3 9.

638

9.75

1 9.

859

9.90

8 10.23

7 10

.284

10.33

2 10

.412

10.58

5 10

.653

10.74

2 10

.800

10.90

8 11

.263

11.33

4 11

.386

11.43

5 11

.509

11.66

9 11

.733

11.81

3 11

.864

11.97

5 12

.324

12.35

6 12

.404

12.45

4 12

.527

12.80

9 12

.856

12.96

5 13

.277

13.31

5 13

.369

13.41

7 13

.490

13.76

4 13

.810

14.20

6 14

.259

14.31

4 14

.364

14.43

9 14

.714

15.13

7 15

.201

15.25

8 15

.308

15.38

6 15

.655

16.07

0 16

.146

16.20

6 16

.336 16

.604

17.00

9 17

.158

17.29

1 17.55

6

18.50

2

19.43

8

20.35

4

21.24

9

22.12

0

22.96

4

23.83

4

24.78

4

25.85

0

Chromatogram (each peak = 1 compound)

min10.2 10.4 10.6 10.8 11

pA

10

20

30

40

50

60


10.

237

10.

284

10.

332

10.

412

10.

585

10.

653

10.

742

10.

800

10.

908

Major constituents were-alkanes (biggest peaks)

This sample had relatively high branched alkanes (some alkenes too)

Other significant constituents are alkenes


• Alkanes – Naming compounds– Linear Alkanes (see table in text – should

know methane to decane)– Branched alkanes

• Example

• Start with longest possible chain• Assign numbers to each carbon• Add branching constituents – name based on

number of carbons added (methane becomes methyl for –CH3) – order is alphabetical


• Questions1. What is the name of CH3CH2CH3? Does it have a

branched isomer?2. What is the name of CH3CHCH3?

CH2CH3

3. Determine the name and formula of the compound given its carbon skeleton structure below:

4. Does the compound in 3) have optical isomers?5. Give the number of Hs attached to Cs at A and B

A

B


• Alkenes– Contain at least 1 carbon-carbon double

bond– Naming (replace –ane ending with –ene

with number referring to end of double bond closest to the #1 carbon)

– Example:• CH3CH=CHCH3 is 2-butene

• Other isomer (CH3CH2CH=CH2) is 1-butene


• Alkenes– Effects of double bonds:

• structural effect – increases melting point temperatures

• makes compounds more reactive/less stable

– Examples in fats, oils and biodiesel– Fats and oils are triglycerides containing

three fatty acids (alkane or alkene in nature)

O

O

O

OCH3

CH3O

CH3O


• Alkenes – Fatty Acid Examples– Fatty acids are linear hydrocarbons with a

carboxylic acid terminus– Size is typically 12 to 22 carbons in length

(18 most common) with 0 to 3 double bonds– Animal fats mostly have 0 double bonds and

are solids at room temperature– Used in biodiesel, these compounds have

high “cloud point” temperatures (gel in fuel tanks at low temperatures)


• Alkenes – Fatty Acid Examples– Most plant fats have fatty acids with double bonds

(cis- isomer) and are liquids at room temperature– Biodiesel made from plant fats has minimal cloud

point problems (but does have some oxidation problems)

– Why? “Kink” from double bonds reduces van der Waals attractions between neighboring hydrocarbon chains, decreasing melting point temperatures

O

CH3OH

O

CH3OH

O

CH3

OH


• Alkenes – Cis – Trans Isomers– Because double bond is a barrier to

rotation, cis- and trans- isomers occur for alkenes

– Example 2-butene can be either cis- or trans-

CH

CH3

C

CH3

H

cis-2-butene trans-2-butene

CCH3

CH3

C

H

H


• Alkenes – Cis – Trans Isomers– Are there differences between cis- and trans-

isomers?– Large differences in melting points for example

between natural plant fatty acids (almost always cis-) and trans- fatty acids formed as a bi-product of hydrogenation (partial conversion from alkenes to alkanes)

– Trans- forms have very small kink vs. cis- fatty acids (and are also known to be unhealthy)

cis- trans-


• Alkenes – In Synthetic Diesel– 1- and 2-dodecene (C12) shown

– Why 2 peaks for 2-alkenes and 1 for 1-alkene?

min10.2 10.4 10.6 10.8 11

pA

10

20

30

40

50

60


10.

237

10.

284

10.

332

10.

412

10.

585

10.

653

10.

742

10.

800

10.

908

1-alkene

2-alkenes

Documents

Chem. 1B – 12/3 Lecture. Announcements I Lab Final –On Wed./Thurs. Next Week –Will be 25 questions, multiple choice –Bring green type scantron (sorry,