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 ID: 930031
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Slide1
Chem. 1B – 11/29 Lecture
Slide2Announcements 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
Slide3Announcements 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)
Slide4Chapter 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
Slide5Chapter 20 Organic Chemistry
Overview
Nature of Carbon – Carbon Bonds
Hydrocarbons (structure, naming and isomers)
Reactions
Aromatic Hydrocarbons
Functional Groups
Slide6Chapter 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 CO
2
+ H
2
O), have negative
D
G
f
º
Carbon “likes to” form 4 bonds ([He]2s
2
2p
2
, but mostly forms
sp
to sp
3
hybrid bonds)
Slide7Chapter 20 Organic Chemistry
Nature of Carbon – Carbon Bonds
Simplest hydrocarbon is CH
4
, methane, in which sp
3
hybridization occurs (tetrahedral geometry
)
As carbon – carbon bonds are common, in alkanes, they also occur with sp
3
hybridization (tetrahedral for each C atom)
Slide8H
Chapter 20 Organic Chemistry
Nature of Carbon – Carbon Bonds
Example alkane with a carbon – carbon bond is ethane
:
CH
3
CH
3
All bonds are sigma bonds in alkanes
This means constituents may rotate about bond
C
H
H
C
H
H
H
H
C
H
H
C
H
H
H
Slide9Chapter 20 Organic Chemistry
Nature of Carbon – Carbon Bonds
Hydrocarbons containing double bonds are known as alkenes
Hybridization is sp
2
(see
ethene
structure below – drawn in 3D) so all atoms in one plane
C
H
H
C
H
remaining p orbital forms
p
bond
Because of
p
bond, rotation about C-C axis doesn’t occur at room temperature
H
Slide10Chapter 20 Organic Chemistry
Hydrocarbon Structures
Linear alkanes: CH
3
(CH
2
)
n
CH
3
Carbon skeleton structure
Example butane =
Only bonds shown as lines and carbons as kinks (Hs omitted)
No.
Carbons
name
1
Methane2Ethane3Propane4n-Butane
5n-Pentane
Slide11Chapter 20 Organic Chemistry
Hydrocarbon Structures
Branched structures:
Example
isobutane
= CH
3
CHCH
3
CH
3
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
Slide12Chapter 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, -CH
3
, -C
2
H
5
, and -C
3
H
7
Slide13Chapter 20 Organic Chemistry
Hydrocarbon Structures
Branched structures:
Example
isobutane
= CH
3
CHCH
3
CH
3
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
Slide14Chapter 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)
Slide15Chapter 20 Organic Chemistry
Some Questions
Which of the following skeleton structures corresponds to n-hexane?
Which pentane isomer will have the lowest boiling point?
Slide16Chapter 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 (C
5
H
10
) is NOT an isomer of n-pentane or isopentane (C
5
H
12) as it has 2 fewer Hs
Slide17Chapter 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:
C
n
H
2n
O
n
+ heat CO(g) + H
2
(g) and
CO(g) + H
2(g) + catalyst H2n+2Cn (various) + H2O(l)
Slide18Chapter 20 Organic Chemistry
Contract Research Example
My job (or that of students working for me) was to determine H
2n+2
C
n
(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)
Slide19Chapter 20 Organic Chemistry
How did we determine the composition of the diesel fuel? Gas chromatography (similar to paper chromatography lab – not done)
Chromatogram (each peak = 1 compound)
Major constituents were-alkanes (biggest peaks)
This sample had relatively high branched alkanes
(most of yellow peaks)
Other significant constituents are
alkenes (green peaks)
C16
Slide20Chapter 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 –CH
3
) – order is alphabetical
Slide21Chapter 20 Organic Chemistry
Questions
What is the name of CH
3
CH
2
CH
3
? Does it have a branched isomer?
What is the name of CH
3
CHCH
3
?
CH
2
CH3Determine the name and formula of the compound given its carbon skeleton structure below:Does the compound in 3) have optical isomers?Give the number of Hs attached to Cs at A and B
A
B
Slide22Chapter 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:
CH
3
CH=CHCH
3
is 2-butene
Other isomer (CH
3
CH2CH=CH2) is 1-butene
Slide23Chapter 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)
Slide24Chapter 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)
Slide25Chapter 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
Slide26Chapter 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-
C
H
CH
3
C
CH
3
H
cis-2-butene
trans-2-butene
C
CH
3
CH
3
C
H
H
Slide27Chapter 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-
Slide28Chapter 20 Organic Chemistry
Alkenes – In Synthetic Diesel
1- and 2-dodecene (C12) shown
Why 2 peaks for 2-alkenes and 1 for 1-alkene?
1-alkene
2-alkenes