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MCAT - Organic Chemistry > Class 1 > Flashcards

Class 1 Flashcards

1
Q

When is a molecule unsaturated?

A

When there is at least 1 pi bond or ring
1 pi bond = 1 degree of saturation
2 pi bonds = 2 degrees, etc.

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2
Q

How do you calculate degree of unsaturation?

A

DOU = (2n + 2 - x)/2

n= number of carbons
x= number of hydrogens
  1. Treat halogens like hydrogens
  2. Ignore oxygens
  3. Subtract the number of Nitrogens from x and then apply
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3
Q

What are properties of unstable molecules

A

High in energy
Reactive with environment
Shorter lifetimes

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4
Q

What are properties of stable molecules

A

Low in energy
Less reactive with environment
Longer lifetimes

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5
Q

What is the ideal bond angle?

A

109.5 degrees, smaller than that = ring strain

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6
Q

What is the typical donating group/subsitituent?

A

Alkyl group

As such, alkyl R groups will push electrons away and thus stabilize a cation and destabilize an anion.

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7
Q

What are typical withdrawing (EN) groups?

A

O, N, halogens

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8
Q

What are three principles about resonance structures?

A
  1. Generally, more resonance structures = greater stabilization
  2. Delocalization can only occur through ADJACENT p orbitals!
  3. Lowest energy (most stable) resonance structures contribute most to hybrid
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9
Q

What three factors indicate the best resonance structure?

A
  1. The octet rule satisfied for ALL atoms!!!!!!!!
  2. The least formal charge
  3. Neg charge on more EN atoms
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10
Q

What is the most stable type of cation?

A

Tertiary!

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11
Q

What is required to have resonance structures?

A

A pi bond!

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12
Q

What defines a Bronsted-Lowry acid?

A

Wants to donate a H+ and leave behind a conjugate base.

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13
Q

What 3 factors affect acid strength and how?

A

By stabilizing the conjugate base:

  1. Electronegativity -> more EN atoms handle negative charge better.
  2. Resonance structure for anion conjugate base
  3. Induction
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14
Q

What is a Lewis base?

A

Nucleophile (negatively charged an/or lone pair of e- to donate)

Think LEWis NUcleophile

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15
Q

Nucleophiles are Lewis ________.

A

Bases

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16
Q

What are some nucleophilic trends?

A

When comparing the same atom, a negative charge makes a stronger nucleophile

For atoms in the same row, nucleophilicity increases as electronegativity DECREASES

For atoms in the same column, nucleophilicity increases as size increases (down the periodic table)

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17
Q

Electrophiles are typically electron ______.

A

Deficient

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18
Q

Electrophiles are Lewis ______

A

Acids

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19
Q

What are abbreviations of some good leaving groups? What makes them good LGs?

A

Tosylate (TsO-)
Mesylate (MSO-)
Acetate (ACO-)

Good LGs because they have lots of resonance

20
Q

What makes something a good LG?

A
  1. Resonance

2. Weak base (e.g. Cl-

21
Q

What is another name for a structural isomer?

A

Constitutional

22
Q

What is a structural (constitutional) isomer?

A

Same molecular formula, but different connectivity

23
Q

What is a conformational isomer?

A

Differ by rotation about a sigma bond (but same molecular formula and connectivity…because of this they have the same chemical and physical properties).

Cannot be isolated

24
Q

In a Newman projection, equal spacing of group is called what?

A

Staggered conformation

25
Q

In a Newman projection, unequal spacing (“covering” of each other) of groups is called what?

A

Eclipsed conformation

26
Q

What is the difference between anti, gauche, and syn conformation?

A 
Anti = 90 deg apart
Syn = right on top of each other
Gauche = in between
27
Q

Is axial or equatorial positioning more stable for bulky groups?

A

Equatorial

28
Q

What is chirality?

A

A molecule with no plane of symmetry, its mirror image is not superimposable.

29
Q

What makes something a chiral center?

A
  1. Sp3 hybridized
  2. All bonds must be to different substituents
  3. Tetrahedral geometry
30
Q

Is a chiral center a stereocenter?

A

Yes

31
Q

What is another name for clockwise rotation?

A

Dextrotatory

32
Q

What is another name for counter-clockwise rotation?

A

Levorotatory

33
Q

What is the key rule about assigning R-S configurations?

A

Atoms with the highest atomic number take priority

34
Q

Clockwise = an ________ configuration.

A

R

35
Q

Counter-clockwise = an ________ configuration.

A

S

36
Q

What is a stereoisomer?

A

Same atomic connectivity
Different spatial arrangement of substituents – usually around chiral centers

e.g. enantiomer

37
Q

What is an enantiomer?

A

Non-superimposable mirror images

Each enantiomer has the opposite configuration at ALL chiral centers

Each enantiomer has optical rotation of equal magnitude, but opposite sign

They have identical chemical and physical properties!! (but are optically different, opposite of each other in fact).

38
Q

What is a racemic mixture? Is it optically active?

A

50:50 mix of enantiomers

Will not be optically active?

39
Q

What is resolution?

A

The process of separating enantiomers

40
Q

What are diastereomers?

A

Nonsuperimposable, NON MIRROR IMAGES
Opposite configuration for at least one, BUT NOT ALL chiral centers

Different chemical and physical properties…can be separated! Obviously different optically as well.

41
Q

What is a geometric isomer?

A

A subset of diastereomers
Restricted in rotation about a double bond or ring
Does not require chiral centers
ALL chemical and physical properties are different

e.g. E vs Z

42
Q

Cis configuration is equivalent to ____ configuration.

A

Z

think Zame (same) side

43
Q

Trans configuration is equivalent to ____ configuration.

A

E

They’re on the Epposite (opposite) side

Generally trans is more stable than cis, but not always

44
Q

What is an epimer?

A

Subset of diastereomers that differ in configuration at ONLY ONE chiral center

45
Q

What is required for a compound to be mesoi

A

Must contain an even number of chiral centers

Must contain an internal plane of symmetry

Symmetrical chiral centers MUST have opposite configurations, thus are not optically active! Kinda like gluing R and S together

46
Q

What types of substituents will increase acidity of a compound?

A

EWG groups (e.g. N, O, etc.)

47
Q

When naming compounds do you list substituents alphabetically?

A

Yes!

MCAT - Organic Chemistry (5 decks)

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