CHEM 30B
Dr. R. Rinehart EXAM
1 Study Guide 2/23/02
READ
THIS GENERAL STATEMENT CAREFULLY:
Your mission in this course is to obtain for yourself a useful
working knowledge and understanding, at an appropriate level, of some basic
organic chemistry and biochemistry, as outlined in the syllabus and subsequently
elaborated in class. The resources available to you include: the text, lectures
and class handouts -- now posted on this site, laboratory exercises, references in print and
on the internet, consultation with the instructor outside of class, tutors
on duty in PS-205, or by arrangement, and whatever other legitimate means are
necessary. There is no easy path to success. Put the work in. It is
particularly important to pay attention to the following sections at the end of
each chapter: Concept Summary, Learning Objectives, Key Terms
and Concepts, and Key Reactions. In particular, the learning objectives
tell you what types of knowledge you will be expected to demonstrate.
You will not be able to demonstrate them unless
you understand the principles involved! Similarly, you will
find it pointless to memorize key terms without knowing what they mean
and how they can be applied.
“Right, sure, yeah, yeah, yeah – just tell us what’s going to be on the test, doc.”
What? Questions designed to show if you have learned to use these principles and their associated language.
How? Generally by means of objective questions in a variety of formats: fill-ins, short answers, matching, multiple choice, true-false, listing, categorizing, prioritizing, and problem-solving are all possibilities. Naming compounds, drawing structures and/or diagrams, writing (and sometimes balancing) equations, and making rational deductions are all possibilities.
Chapter
11: Alkanes, Cycloalkanes, and Haloalkanes [also Intermolecular Forces &
Chime workshops on alkanes]
covalent bonding : shared pairs of e-
C: normally
forms 4 covalent bonds; H and X form 1;
O and S form 2; N usually forms 3.
hydrocarbons: contain C and H only
hybridization: C = 1s22s22px12py12pz0
,
but this does not explain observed molecular geometry;
∴ we mathematically mix the 2s and 2p orbitals in
various ways to get a better description.
sp3
hybridization ⇒
4 identical sp3 orbitals with tetrahedral geometry,
109o28’ bond angles
skeleton
formula: all H’s on C not shown; saves time in writing and looking
at complex structures
structural isomers: same
molecular formula, different pattern of bonding.
Results in
different compounds with different physical, chemical, and biological
properties.
physical properties: observed/measured parameters used to
characterize compounds.
Include: melting point, boiling point, solubility in water and
in other solvents, color, odor,
density,
electrical conductivity, crystal structure, heat of
formation, heat of fusion,
heat of
vaporization, refractive index, specific rotation of polarized light,
infrared
spectrum, etc……….
Many of these properties are determined by the type and strength of the intermolecular
attractive forces between the particles involved. Hence,
understanding the types of
such forces, how they originate, and how they operate is very important.
The
strongest force available generally determines what happens in a system.
ionic attractions: between oppositely-charged ions. Very strong;
strength depends on size of charge,
distance,
shielding by solvent, etc.
hydrogen bonding: special
type of interaction between a H bonded to an electronegative atom
such as O
or N and the lone pair of electrons on a second electronegative
atom.
Stronger than the next two
forces. H-bonding substances can always have dipolar attractions present also,
but the reverse statement not true. Important in water, alcohols, proteins,
DNA.
dipolar attractions: dipoles form when two covalently-joined atoms
have a substantial difference
in electronegativity. A dipole is the electrical analog of a
magnet. Opposite poles attract.
Generally stronger than
dispersion forces.
London or dispersion
forces: very weak; caused by synchronization of random electron
movements
in neighboring molecules via electrical fields. Strongest when there is
extensive
surface
area of contact. Most significant in nonpolar compounds. Associated with
“hydrophobic”
substances.
The three weak forces [H-bonding,
dipolar forces, and dispersion forces are collectively referred to as
van der Waals forces]
nomenclature: Nx for alkanes
is the basis for Nx of all other classes of compounds.
Based on the
Greek words for the number of C’s in the longest
“straight” chain;
-ane
is characteristic ending. Prefix cyclo- used for compounds
with rings.
location on
chain
specified with numbers [“locants,” use one for each substituent].
chemical properties:
the set of characteristic chemical reactions
which a substance exhibits.
characteristic reaction
of alkanes and cycloalkanes:
(complete)
combustion CxHy
+ (x + ¼y) O2 à
x CO2 + ½y H2O
(+ heat
and maybe light)
[this works
for ANY HC] If sufficient
O2 not present, some CO forms (incomplete)
natural sources of alkanes : petroleum
(C5 – C100+) and natural gas (C1 – C4).
Supply
running low!!!!!
Prices going
up!!!!!!!!! Wars being fought [and planned?]...
[also Lab & Chime workshop
on unsaturated hydrocarbons]
Collectively these hydrocarbons are called
“unsaturated” [with H] because they can be forced to add H2
Alkenes contain double bonds between C’s; for one C=C,
molecular formula = CnH2n
sources: 1) petroleum
and natural gas 2) thermal
“cracking” of alkanes
3) dehydration of alcohols
4) treatment of alkyl
halides with strong bases
sp2
hybridization ⇒
3
identical sp2
orbitals with
planar geometry, 120o bond angles;
pz remains
Characteristic reactions:
addition
·
of H2 catalytic
hydrogenation: gives alkanes
·
of X2
halogenation: gives vicinal dihalides
[reaction
causes orange color of Br2 to disappear – used as test for C=C]
·
of HX hydrohalogenation: gives monohalides
·
of H2O hydration:
gives alcohols
·
of C=C: leads
to polymerization à
polyethylene, polypropylene, polystyrene, PVC,
·
react with purple KMnO4 to give brown/black MnO2
ppt [another test for C=C]
Alkynes contain
triple bonds between C’s; for one C≡C, molecular formula = CnH2n-2
sp hybridization
⇒
2
identical sp orbitals
with linear geometry , 180o bond angles; {+
py & pz}
Aromatics
every
ring C is sp2 bond
angles 120o
“resonance”
from
delocalized electrons ⇒ more stable than alkenes, react differently
uses:
solvents, starting materials in syntheses; essential
components in some biomolecules;
aromatic hydrocarbons are toxic:
bone marrow depressants, carcinogens, drugs of abuse [glue]
Chapter
13: Alcohols, Phenols, Ethers, Thiols [also Lab/workshop on alcohols]
Classes: 1o, 2o, 3o
react differently
Nx:
attach suffix –ol
to stem name of longest chain containing the –OH, which gets lowest number
physical properties: C1-C3 miscible with
H2O, C4-C6 soluble in H2O,
>C6 insoluble in H2O
relatively high melting and boiling points due to H-bonding
soluble in other alcohols, ethers, acetone, etc.
sources: natural: wood à
methanol; fermentation à
ethanol; synthesis by
hydration of alkenes
uses: solvents, antifreeze, moisturizer, flavorings, booze
characteristic reactions:
oxidation:
complete = combustion;
incomplete: 1o à
aldehydes à
carboxylic
acids, 2o à
ketones, 3o N.R.
dehydration: acid-catalyzed; at 140oC, intermolecular
2ROH à
ROR + H2O
at 180oC, intramolecular
RCH2CHOHR’ à
RCH=CHR’ + H2O
Phenols: contain the
hydroxyl group attached to C in an aromatic ring
ArOH
uses: disinfectants, wood preservatives, embalming agents, antioxidants
Ethers: contain
oxygen between two alkyl or aryl groups
ROR’
formed by dehydration of alcohols at 140oC
physical properties: somewhat polar
chemical properties: relatively inert
but the low-mw ones are
highly flammable
uses: solvents, general anesthetics, gasoline additives
Thiols: contain the thiol (a.k.a.
sulfhydryl or mercapto) group attached to C in an alkyl group
RSH
highly odoriferous: skunk essence, onions, garlic, etc.
characteristic reactions: oxidation to form disulfides: 2 RSH + {O} à
RS-SR
reaction with heavy metals: 2
RSH + M2+ à
(RS)2M + 2H+
both rxns important in protein chemistry
Multifunctional compounds: have more than one type of functional group, belong to several classes
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© Ronald W. Rinehart, 2002, 2003