Chem. 1B – 12/3 Lecture
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
Chapter 20 Organic Chemistry
• Overview– Nature of Carbon – Carbon Bonds– Hydrocarbons (structure, naming and
isomers)– Reactions– Aromatic Hydrocarbons– Functional Groups
Chapter 20 Organic Chemistry
• 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)
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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)
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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)
Chapter 20 Organic Chemistry
• 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)
Chapter 20 Organic Chemistry
• 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
FID1 B, (YVONNE\08081301.D)
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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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)
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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
Chapter 20 Organic Chemistry
• 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-
Chapter 20 Organic Chemistry
• 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
FID1 B, (YVONNE\08081301.D)
10.
237
10.
284
10.
332
10.
412
10.
585
10.
653
10.
742
10.
800
10.
908
1-alkene
2-alkenes