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Fall2023 > OChem Exam 1 > Flashcards

OChem Exam 1 Flashcards

1
Q

Isomers

A

compounds that are constructed from the same atoms (and molecular formula) but differ from each other
1. constitutional
2. stereoisomers

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2
Q

constitutional isomers

A

same formula, differ in order of bonding

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3
Q

stereoisomers

A

same formula, different in 3D arrangement

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4
Q

cis

A

same side of double bond

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5
Q

trans

A

opposite side of double bond

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6
Q

chiral

A

a molecule that is not superimposable (able to be laid upon) of its mirror image

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7
Q

achiral

A

a molecule is superimposable on its mirror image

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8
Q

enantiomer

A

a non-superimposable mirror image of a compound (same physical properties)

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9
Q

diastereomer

A

non-superimposable and NOT mirror images (has different physical properties; cis-trans isomers)

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10
Q

meso compound

A

has reflectional symmetry and is achiral even with chiral centers (has a plane of symmetry)

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11
Q

chiral molecule

A

has the ability to rotate plane-polarized light

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12
Q

chiral center

A

tetrahedral atom attached to 4 different substituents

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13
Q

hyperconjugation

A

donation of one electron density from an adjacent sigma bond to stabilize an electron-deficient pie system

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14
Q

Name the steps to drawing a lewis structure

A
  1. count total number of valence electrons (based on group number)
  2. pick central atom (most EN)
  3. build sigma bidn framework
  4. fill outer octets (most EN first)
  5. remaining lone pairs on central atom
  6. make pi bonds if central atoms does not have octet
  7. assign formal charges (circle)
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15
Q

How to calculate formal charges

A

valence electrons (PT number) - electrons “owned” (e on structure)

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16
Q

define electronegativity

A

the tendency of an atom, in a covalent bond, to draw electron density towards itself.

*most EN atom is F, as EN increases up a group and across a row

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17
Q

lewis structure exceptions

A
  • odd number of electrons
  • expanded octet (common on P, S, Cl, Br, I)
  • unfilled octet on central atom (common on transition metals)
  • oxyacids (H leading with many Os- H are attached to outer atoms, not central atom)
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18
Q

How to find the most polar molecule?

A
  • The greater the electronegativity difference, the more polar the bond.
  • linear and symmetrical molecules tend to be nonpolar, while asymmetrical molecules tend to be polar.
  • If the individual bond dipoles within the molecule do not cancel each other out due to symmetry, the molecule will have a net dipole moment, making it polar.
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19
Q

Define polarizability

A

the ability of an electron cloud to distort in response to the approach of a point negative charge

*most polarizable is bottom left because larger molecules are more polarizable where electrons can move away in the cloud from approaching negative charge

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20
Q

Line structure vs condensed formula

A

line structure: each point is an assumed carbon
condensed formula: shows no bonds. for branches: main(branch)continue

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21
Q

rings or acyclic structures can be abbreviated, how?

A

as Ph-
*put “letter -“ in front of a formula to indicate ring formation like o, m, or p

22
Q

p-

A

para– 1,4 arrangement

22
Q

m-

A

meta— 1,3 arrangement

23
Q

o-

A

ortho– 1,2 arrangement

24
Q

Bronsted-Lowery Acids and Bases defintion

A

acid= proton donor
base= proton acceptor

(H+ is a proton)

25
Q

Lewis acid and base definition

A

acid: electron pair acceptor (electrophile)
base: electron pair donor (nucleophile)

26
Q

Luse Flood acid and base definition

A

acid: oxide acceptor
base: oxide donor

27
Q

What are the 4 factors that influence acid strength? (in the order of importance)

A
  1. resonance
  2. polarizability
  3. electronegativity
  4. s-character
28
Q

explain how resonance impacts acid strength

A

more oxyegn= more resonance= stronger acid due to a stable anion

29
Q

explain how polarizability impacts acid strength

A

bigger atom= lower-left corner of PT= stronger acid

30
Q

explain how electronegativity impacts acid strength

A

more EN= upper right PT= more positive nucleus= electrons held tighter= stronger acid

31
Q

explain how s-character impacts acid strength

A

s-character= orbital size= small orbitals hold electrons tighter= stronger acid

32
Q

How to draw 6 Newman projections for a molecule

A
  1. choose a bond to look down and orient
  2. Draw Front Carbon: dot
  3. Draw Rear Carbon: Larger circle
  4. Position Substituents
  5. rotate the front carbon by 60 degrees each time
  6. ID most and least stable
  7. rank in stability and put on an energy diagram
33
Q

define Torsional Strain

A

close electron clouds, like in eclipsing conformation, cause repelling

*gauche torsional strain: non H compounds are next to each other and not eclipsed

34
Q

define steric strain

A

intersection of electron clouds causes strain

35
Q

define transannular strain

A

when 2 groups point at each other from across a ring with an even number of carbons (chair conformation)

36
Q

how to number a carbon ring

A

based on the most highly oxidized carbon (more O) or the higher priority substituent

37
Q

how to find the most stable chair

A
  • sp3 hybridized atoms (alkyl groups - CH3) have the highest strain
  • sp2 hybridized (acids, ester)
  • nitrogen and oxygen substituents
  • halogens

*most energy and biggest substituent has associated with 1,3 diaxial strain– preference for equatorial position

38
Q

name the 1-10 carbon prefixes for naming

A

1– meth
2– eth
3– prop
4– but
5– pent
6– hex
7– hept
8– oct
9– non
10- dec

39
Q

Steps of Free Radical Chain Mechanism

A
  1. Initiation: formation of free radicals by breaking a covalent bond, often through heat or light. Cl₂ → 2 Cl*
  2. Propagation: repeated step involves the successive generation and consumption of free radicals– creating new radicals in the process. CH₄ + Cl* → CH₃Cl + H*
  3. Termination: involves the combination of two free radicals to form a stable molecule, thereby removing radicals from the chain. 2 Cl* → Cl₂
  4. Overall: CH₄ + Cl₂ → CH₃Cl + HCl and H△ rxn overall

*don’t forget to show fish hook arrows for electron movement and hv above the rxn arrow

40
Q

Define the Hammond postulate

A

“If two states, as for example, a transition state and an unstable intermediate, occur consecutively during a reaction process and have nearly the same energy content, their interconversion will involve only a small reorganization of molecular structure”

TLDR: close in energy= close in structure

41
Q

steps for naming an enantiomer

A
  1. find chiaral centers
  2. number based on priority (atomic number)
  3. rearrange so 1 is coming out and 4 is going back
  4. connect 1 to 2 to 3 in 3D
  5. clockwise = R and counterclockwise = S
42
Q

calculating enantiomeric excess %

A

Enantiomeric excess (ee): the amount of pure isomer after subtrating out the racemic part

ee (%) = ([specific rotation]measured / [specififc rotation]pure) x 100%

  • higher ee% indicates a greater purity of the desired enantiomer
43
Q

Steps to pick the best chair conformation and calculate the approximate ratio of the two

A
  1. draw as a ring and make chairs
  2. ID strain and use given ΔG to find most and least stable
  3. find ΔGrxn = more - less
  4. use answer in Keq equation
  5. solve Keq to get answer to plug into Keq = Product/Reactant
  6. plug that answer into product + reactant = 1.0
  7. convert decimal to percent

Gibbs free energy (ΔG):
R is the ideal gas constant– 8.314 J/(mol·K)
T is the temperature in Kelvin (298 K).

Keq = e^(-ΔG° / (RT)) *delta G is NEGATIVE

Keq = [products] / [reactants]

[products] + [reactants] = 1.0

44
Q

make a resolution (separation of a racemic mixture) flow diagram

A
  1. racemic mixture (enantiomers) with the same physical properties
  2. use optically pure reagent to separate mixture into diastereomers with different physical properties
    - amine (N-H) group’s electron pair interacts with the reagent
  3. separate diastereomers and cleave them into pure isomers and reagents
  4. recover reagents for reuse or throw away
45
Q

define racemic mixture

A

a 1:1 mixture of enantiomers that rotates plane-polarized light

46
Q

define what a C2 axis of symmetry is

A

if you perform a half-turn rotation (180 degrees) around the C2 axis, the object will superimpose onto its original orientation

47
Q

name the 3 ways to separate or do the resolution of enantiomers

A
  • crystalization (physically separate)
  • chiral resolving agents (use a reagent and separate diastereomers)
  • column chromatography (separate by interaction (may stick) with a column of medium)
48
Q

define conformational isomer

A

a stereoisomer that can be interconverted by rotating about sigma bonds (no bond breaks)

49
Q

what types of strain cause one conformation isomer to be higher in energy than another?

A
  • eclipsing torsional strain
  • gauche torsional strain (60 degree dihedral angle)
  • eclipsing steric strain
50
Q

recreate relative reactivity chart

A

F2 Cl2 Br2
1- 1.0 1 1
2- 1.2 4 80
3- 1.4 5 1700

51
Q

how to find a specific rotation

A

[a]specific = ([a]observed x100) / ( ℓ x c)

ℓ= length of polarimeter in dm
c= concentration in grams/dL

Fall2023 (10 decks)

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