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CHEM 3311- Midterm Exam Guide - Comprehensive Notes for the exam ( 23 pages long!)


Department
Chemistry
Course Code
CHEM 3311
Professor
Douglas Gin
Study Guide
Midterm

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CU-Boulder
CHEM 3311
MIDTERM EXAM
STUDY GUIDE

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Organic Chemistry Midterm Study Guide
Set 1: Lewis Structures, Resonance and Functional Groups
Lewis Structures and Resonance:
Lewis structure: shows atoms and valence electrons in outermost shell used in bonding
o Central atom is usually least electronegative (exception: H)
Resonance: arises when there is more than one reasonable Lewis structure for a given molecule
o In structures that exhibit resonance, electrons are delocalized means that they are not confined to a particular region, i.e., an atom or
bond they are more spread out
o The resonance contributors taken together make up a resonance hybrid: overall description of a molecule, all contributors together
o Rule for making resonance structures: don’t move electrons toward sp3 carbon violates octet rule
Formal charge: Formal charge = valence e (nonbonding e + bonds)
Curved arrow notation:
o Shows the movement of electrons, either real (in a rxn) or imaginary (resonance)
o In the case of resonance, it is imaginary movement electrons are not “moving,” they are delocalizing/spreading out over a larger area
Assessing contributors to the resonance hybrid:
o Octet rule: most important! Is the octet rule satisfied for all elements that need an octet?
It’s ok to have (+) charge on most electronegative atom as long as octet rule is satisfied (usually on O or N)
o Minimizing the number and magnitude of formal charges: how many formal charges that are not zero and the size of the charge
(+1/-1 vs. +2/-2)
o Placing negative charge on the most electronegative atom
o Minimizing separation of charge
Among all the contributors to a resonance hybrid:
o All atoms stay in exactly the same place
o All bond angles stay the same for all contributors
o Net charge for all contributors stays the same
Resonance in allylic systems
o Allyl cation: Allyl anion:
o Allylic radical: use fishhook arrows, since electrons are moving singly (not in pairs)
Radical unpaired electrons at allylic position
Resonance in benzylic systems
o Benzylic systems: use the same patterns as you saw in allylic systems - the structure that retains the intact benzene ring is always
the major resonance contributor
o Benzylic cation: Benzylic anion:
o Benzylic radical:
Functional Groups:
A functional group is a group of atoms (or a single atom) in an organic molecule that has a characteristic reactivity (way of reacting)
Hydrocarbons (contain C, H only):
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Organic Chemistry Midterm Study Guide
o Aliphatic hydrocarbons:
Alkanes: hydrocarbon it all single bonds, all carbons have sp3 hybridization, “saturated hydrocarbon”
Classification:
1° (primary) carbon attached to 1 C
2° (secondary) carbon attached to 2 C
3° (tertiary) carbon attached to 3 C
4° (quaternary) carbon attached to 4 C
Alkenes: hydrocarbon with at least one CC double bond
Alkynes: hydrocarbon with at least one CC triple bond
o Aromatic hydrocarbons: presence of a benzene ring
Alkyl halide (RX):
Alkyl group + halogen (F, Cl, Br, I)
Classification: same method as sp3 carbons based on what kind of sp3 carbon the halogen is attached to (1°, 2°, 3°, or 4° RX)
Alcohol (ROH):
Hydrocarbon with OH
NOT an alcohol: Carboxylic acid
Ether (ROR):
Special case: Epoxide 3 members ring with 2 C’s and 1 O
Aldehyde (RCHO):
Ketone (RCOR):
Carboxylic acids (RCOOH):
Carboxylic acid derivatives are compounds that produce carboxylic acids when reacted with water (hydrolysis):
o Acid Halides:
o Anhydrides:
o Esters:
o Amides:
Amines:
H can be replaced by R
Classification: based on how many C’s are directly attached to N
Nitriles (RCN):
R must be an alkyl group
Nitro compounds (RNO2):
Ex:
Constitutional (Structural isomers):
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