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Org Chem 1 > Exam 1: > Flashcards

Exam 1: Flashcards

Structures, resonance, acid base chemistry

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1
Q

What do structural formulas do and what are the types?

A

Represent different chemical compounds
Lewis, condensed, and line-angle “skeleton/stick figure” structures

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2
Q

What is the concern of organic chemistry with regards to compounds?

A

The reactivity of compounds

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3
Q

What must you do when drawing Lewis structures?

A

Show all atoms, bonds, and lone pairs (radicals)

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4
Q

What must you do/can you leave out when using condensed structures?

A

Don’t show individual bonds
Electrons are implied
Show all atoms, providing bonds/electrons to satisfy octet rule
-assume neutral unless formal charge specified

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5
Q

What are the special abbreviations for condensed structures?

A

-CHO: -C(=O::)-H
-COOH = -CO2H = -C(=O::)-O::-H

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6
Q

What are the rules of line-angle structures?

A

Every vertex is a carbon
H’s on C are implied
H’s on heteroatoms shown
lone pairs optional (helpful @ beginning)
Bonds are shown

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7
Q

What is the rule of formal charges and structures?

A

For ALL structures must show non-zero formal charge & radicals (unpaired electrons)

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8
Q

What is resonance? Why are there resonance structures?

A

When electrons are shared over the molecule (between 3+ atoms) the electrons are delocalized. It adds stability (Lowers the energy) of a molecule
Structures because resonance cannot be shown well on one structure

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9
Q

What are the resonance structure symboles?

A

[] surround resonance
three line equal sign to hybrid
<–> resonance arrow: two molecules are different representations of the SAME molecule
curved arrows show electron flow/movement. They originate from the electrons to where they are moving to (start from lone pair or bond)
- double barb: two electrons
- single barb “fishhook”: single electron

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10
Q

What are the rules of resonance structures?

A

Move electrons not atoms
Make correct structures
You can move pi bonds to adjacent bonds or atoms
Can move lone pairs to pi bonds
Overall charge remains same
Cam move multiple electron pairs at once

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11
Q

What are considered correct resonance structures?

A

C, B, Al are ok with a sixtet
N, O, F need an octet (unless they are radicals)
2nd row elements cannot have more than an octet

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12
Q

What affects the reactivity of resonance molecules?

A

Both major and minor resonance structures

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13
Q

What is the real resonance structure?

A

The structure that looks most like the major contributors. The most stable state (lowest energy)

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14
Q

How can you tell what is a major or minor resonance contributor?

A

IN Order
1) draw all resonance structures (no short cut, only practice will tell you when you are done)
2) All octets filled-better
3) More bonds-better
4) Lowest charge separation-better
5) Charges stabilized
Look at periodic table
-negative: across: more electronegative (–> F)
down: larger atom more stable
-positive: opposite

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15
Q

What is an example of a minor residence structure so minor we do not note it?

A

negative FC on one C and positive FC on the C it is bonded to

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16
Q

How is -CO2- written as a structure?
How is -CC- written as a structure?

A

C double bond O single bond O
C triple bond C

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17
Q

What does it mean when carbon has a positive, neutral, or negative charge?

A

Positive: three bonds only (sixtet)
Neutral: four bonds
Negative: three bonds and long pair of electrons

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18
Q

What does it mean when boron has a positive, neutral, or negative charge?

A

Positive: NA
Neutral: three bonds only (sixtet)
Negative: four bonds

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19
Q

What does it mean when nitrogen has a positive, neutral, or negative charge?

A

Positive: Four bonds
Neutral: three bonds and lone pair
Negative: two bonds and two lone pairs

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20
Q

What does it mean when oxygen has a positive, neutral, or negative charge?

A

Positive: Three bonds, one lone pair
Neutral: two bonds, two lone pairs
Negative: one bone three lone pairs

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21
Q

What does it mean when halogens have a positive, neutral, or negative charge?

A

Positive: Two bonds two lone pairs
Neutral: One bond, three lone pairs
Negative: four lone pairs

22
Q

What is the periodic table of elements that you need to know for O-chem?

A

H, He, Li, Be, B, C, N, O, F, Ne,
below C: Si, P, S, Cl
below Cl: Br then I

23
Q

What is the purpose of orbital hybridization?

A

Hybridization give the molecular shapes and the bond angles

24
Q

What are the three hybridization orbitals used? How many of them? What shape to they make and what is their bond angle?

A

sp: 2x, linear, 180*
sp2: 3x, trigonal planar, 120*
sp3: 4x, tetrahedral, 109.5* (a little smaller with lone pairs –> bent)

25
Q

What things of an atom use hybridized orbitals?

A

Sigma bonds (direct overlap) and lone electrons

26
Q

What are the differences between sigma and pi bonds?

A

Sigma: one in every bond, allows rotation,
pi: one in double bond, two in triple bond, restricts rotation, both lobes of p orbital must overlap

27
Q

What must you think when you see lone pairs and pi bonds adjacent?

A

Resonance: if the structure has a resonance that has a lower hybridization (sp or sp2) that will be the shape of the molecule and the angle of the bonds
has to be to share e-

28
Q

What are the two types of isomers?

A

Constitutional isomer: “structural” different bonding “connectivity” same molecular formula
Stereoisomers: Same molecular formula and connectivity different orientation in space

29
Q

What type of stereoisomers are we concerned with?

A

Geometric: cis - like groups same side, trans - like groups opposite side
works for one double bond and rings

30
Q

What are the three types of acid bases?

A

Arrhenius: A: H3O+, B: OH-
Bronsted-Lowry: A: proton donor, B: proton acceptor
Lewis: A: electron pair acceptor B: electron pair donor

31
Q

How does O-chem relate to the different definitions of acids and bases?

A

O-chem’s definition is Bronsted-Lowry which includes Arrhenius. Lewis acids are called electrophils (love electron) while L bases are called nucleophils (love nucleus)

32
Q

What are the relationships between acids, bases, and their conjugates?

A

The acid will donate a proton to become a conjugate base
The base will accept a proton to become a conjugate acid

33
Q

What is the relationship between pH and pka and the strength of an acid?

A

The lower the pH and pKa the stronger the acid

34
Q

What is the relationship between pH and pkb and the strength of a base?

A

The higher the pH and pKa the stronger the base

35
Q

What is the equilibrium constant of the acid?

A

Ka

36
Q

How can the tend of the equilibrium in an acid base reaction be determined?

A

Determine which acid (acid or conjugate acid) is the weaker acid because the equilibrium will tend toward weaker acid
Look up pKa on tables

37
Q

Notes for resonance structures:

A

Do not miss moving + or - onto other carbon atoms from pi bonds
Do not miss giving oxygen three electron pairs

38
Q

What is the formula for formal charge?

A

FC= Valence electrons - (lone electrons + 1/2 bonded electrons)`

39
Q

When a pka value is not given what can you use to assume pka values?

A

Look at which base will be the most stable meaning weaker base b/c more able to hold on to electrons. Weaker acid will be on same side

40
Q

What makes a base more stable?

A

More electronegative, larger size, induction, hybridization, resonance.

41
Q

How does electronegativity stabilize a base?

A

atom is most stable when negative charge is on the most electronegative atom

42
Q

What is the electronegativity trend? When can it be used in base stabilization?

A

Left to right and bottom to top (F most EN)
Used across- atoms in same row

43
Q

How does an atoms’ size increase base stabilization?

A

Increased surface area allows paired elections to spread out more increasing stabilization

44
Q

What is the size trend and when can it be used in base stabilization?

A

Increase in size top to bottom. Can be used when atoms in same column/group

45
Q

How is hybridization used in base stabilization?

A

The more s characteristic the more stable sp > sp2 > sp3

46
Q

How is resonance used in base stabilization?

A

If resonance structures are possible the base is more stable because the charge is more spread out.

47
Q

How is acidity correlated with the things that increase base size?

A

Increased acidity with increased electronegativity, size, induction, hybridization (sp), and resonance.

48
Q

What does induction do for base stabilization?

A

When an electronegative atom is near the atom with the negative charge it shares the charge through sigma bonds (supports the atom with the negative charge)

49
Q

What does a negative charge do to an atom?

A

It adds electron density.

50
Q

What are the ranges of the induction effect on atoms?

A

The closer the electronegative atom the greater induction effect. Adjacent EN atoms are a significant help

51
Q

What should you ask when a question asks which proton is more acidic?

A

What is the difference between the protons available? EN, hybridization, induction, size, resonance?

52
Q

What form of base stabilization is the most important?

A

resonance wins

Org Chem 1 (4 decks)

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