Download 11/29 Lecture

Chem. 1B – 11/29 Lecture
Announcements I
• Lab
– Last Lab #15 (yesterday and today)
– Lab #15 Report due next Mon. + Tues
– Lab Final next week (Wed. + Thurs.) – see
syllabus for labs covered – need scantron
• Mastering
– Ch. 20 assignment (Organic Chemistry) due
12/10
Announcements II
• Exam 3
– Thursday
– On Electrochemistry (~55%) and Chapter 24
(~45%)
– Help Session Tues. afternoon (with PALs – I
can do 4:00 to 4:45)
• Today’s Lecture
– Organic Chemistry (Ch. 20)
Chapter 20 Organic Chemistry
• Introduction
– Organic Chemistry is a major area of study
(we offer 7 organic chemistry classes at the
undergraduate level)
– In ~1.5 weeks, 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
DGfº
– 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)
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
H
H
C
H
H
C
H
H
H
H
H
C
C
H
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
remaining p orbital forms p bond
H
H
C
H
C
H
Because of p bond, rotation
about C-C axis doesn’t
occur at room temperature
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.
name
Carbons
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 (constituents are
-H, -CH3, -C2H5, and -C3H7
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 – cont.
•
•
•
Two different (3D) structures can be drawn of 3methyl 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
• Some Questions
1. Which of the following skeleton structures
corresponds to n-hexane?
2. Which pentane isomer will have the lowest
boiling point?
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)
40
20
0
5
7.632
7.723
7.760
7.859
7.940
8.069
8.151
8.349
8.468
8.662
8.969
9.039
9.078
9.125
9.209
9.262
9.472
9.638
9.751
9.859
9.908
10
15
20
25
25.850
20
10.2
min
Chromatogram (each peak = 1 compound)
10.284
10
10.4
10.6
10.800
160
10.742
pA
10.8
10.908
10.653
10.585
10.412
C16
10.332
FID1 B, (YVONNE\08081301.D)
10.237
14.714
1.756
1.824
Major constituents were-alkanes
(biggest peaks)
24.784
23.834
22.964
22.120
21.249
20.354
19.438
18.502
15.137
15.201
15.258
15.308
15.386
15.655
16.070
16.146
16.206
16.336
16.604
17.009
17.158
17.291
17.556
180
11.263
11.334
11.386
11.435
11.509
11.669
11.733
11.813
11.864
11.975
12.324
12.356
12.404
12.454
12.527
12.809
12.856
12.965
13.277
13.315
13.369
13.417
13.490
13.810 13.764
14.206
14.259
14.314
14.364
14.439
10.742
9.573
8.269
6.764
5.013
100
4.378
4.407
4.519
4.594
4.643
4.784
4.858
5.142
5.289
5.658
6.008
6.162
6.292
6.423
6.537
6.626
6.706
6.865
6.994
7.164
80
3.244
120
10.237
10.284
10.332
10.412
10.585
10.653
10.800
10.908
60
2.143
pA
2.737
2.768
2.809
2.884
2.974
3.120
3.184
3.317
3.369
3.504
1.634
1.707
1.961
2.040
2.087
2.194
2.267
Chapter 20 Organic Chemistry
• How did we determine the composition of the
diesel fuel? Gas chromatography (similar to
paper chromatography lab – not done)
This sample had relatively high branched
alkanes (most of yellow peaks)
Other significant constituents are
alkenes (green peaks)
FID1 B, (YVONNE\08081301.D)
140
60
50
40
30
11
min
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
• Questions
1. 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:
A
B
4. Does the compound in 3) have optical isomers?
5. Give the number of Hs attached to Cs at A and 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
CH3
O
H3C
O
O
CH3
O
O
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 (cisisomer) 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
CH3
HO
O
CH3
HO
O
HO
O
H3C
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
transH
H
H
C
CH3
CH3
cis-2-butene
C
C
C
CH3
CH3
H
trans-2-butene
Chapter 20 Organic Chemistry
• Alkenes – Cis – Trans Isomers
–
–
–
Are there differences between cis- and transisomers?
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
1-alkene
FID1 B, (YVONNE\08081301.D)
10.742
pA
2-alkenes
60
50
40
10
10.2
10.4
10.8
10.908
10.800
10.6
10.653
10.585
10.412
10.332
20
10.284
10.237
30
11
min
– Why 2 peaks for 2-alkenes and 1 for 1alkene?