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MCAT > Physics II: 4-6, 9-10 > Flashcards

Physics II: 4-6, 9-10 Flashcards

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1
Q

chemical mechanisms

A

propose a series of steps that make up the overall reaction

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2
Q

intermediates

A

molecules that exist within the course of a reaction but are neither reactants nor products overall

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3
Q

rate determining step

A

slowest step

limits the maximum rate at which a reaction can proceed

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4
Q

collision theory

A

rate of a reaction is proportional to the number of collisions per second between the reacting molecules

(not all collisions result in a chemical rxn)

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5
Q

collision theory

for a collision to be effective…

A

molecules must be in the proper orientation and have sufficient kinetic energy to exceed the activation energy

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6
Q

activation energy

A

Ea

minimum energy of collision necessary for a reaction to take place

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7
Q

collision theory eq

A

rate = Z x f

Z = total number of collisions occurring per second

f = fraction of collisions that are effective

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8
Q

arrhenius eq

A

A = frequency actor

R = ideal gas constant

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9
Q

frequency factor

A

A

aka attempt frequency

measure of how often molecules in a certain reaction collide

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10
Q

Arrhenius eq

relationship between freq factor and rate constant

A

direct relationship

as freq factor inc, rate constant inc

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11
Q

arrhenius eq

exponent relationship

A

as the exponent gets smaller, it becomes less negative -> increases create constant

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12
Q

arrhenius eq

what makes the negative exponent smaller? what does this do?

A

low activation energy and high temp -> inc rate constant

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13
Q

how to increase frequency factor

A

increase number of molecules in a vessel (opportunities for collision are increased)

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14
Q

transition state theory

A

states that molecules form a transition state or activated complex during a reaction in which the old bonds are partially dissociated and the new bonds are partially formed

from the transition state, the reaction can proceed toward products or revert back to reactants

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15
Q

transition state

A

have the highest energy (greater than reactants and products)

old bonds are weakened and new bonds begin to form

theoretical structures that cannot be isolated

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16
Q

free energy change of the reaction

A

ΔGrxn

difference between the free energy of the products and the free energy of the reactants

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17
Q

exergonic reaction

A

-ΔG

energy is given off

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18
Q

endergonic reaction

A

+ΔG

energy is absorbed

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19
Q

exergonic reaction diagram

A
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20
Q

endergonic reaction diagram

A
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21
Q

how do reaction concentrations affect reaction rate?

A

conc of reactants inc, number of effective collisions inc (frequency factor)

reaction rate will increase for all but zero order reactions

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22
Q

how does temperature affect reaction rate?

A

reaction rate inc, temp inc

bc temp is measure of particles’ avg kinetic energy

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23
Q

optimal temp for enzymatic reaction

A

35 - 40 C

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24
Q

how does the medium in which rxn takes place affect reaction rate?

A

depends on how reactants react w medium

polar solvents are preferred bc molecular dipole tends to polarize the bonds of the reactants,, thereby lengthening and weakening them, permitting the reaction to occur faster

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25
Q

how do catalysts affect reaction rate?

A

increase reaction rate without being consumed in the rxn

lowers activation energy for both forward and backward rxn

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26
Q

catalysts

A

increase reaction rate without being consumed in rxn

stabilize reactants so as to reduce the activation energy necessary for the rxn to proceed

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27
Q

homogenous catalysis

A

catalyst is in same phase as reactants

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28
Q

heterogeneous catalysis

A

catalyst is in a different phase from reactants

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29
Q

what do catalysts not affect?

A

free energies of reactants or products or difference between them

don’t change nonspontaneous rxns into spontaneous ones (only make spontaneous ones move quicker)

do not impact equilibrium position or measurement of Keq

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30
Q

how are rate laws determined?

A

experimentally

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31
Q

rate law eq

A

rate = k[A]x[B]y

aA + bB -> cC + dD

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32
Q

eq to determine the order of reactant A experimentally

A

Δrate = Δ[A]x

multiplication factors

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33
Q

zero order reaction

A

rate of formation of product C is independent of change sin concentrations of any of the reactants

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34
Q

zero order reaction

rate law

A

rate = k[A]0[B]0 = k

k units: M/s

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35
Q

ways to change the rate of zero order rxn

A

change temperature, add catalyst

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36
Q

zero order rxn graph

slope

A

conc vs time: linear, k = -slope

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37
Q

first order rxn

A

have a nonconstant rate that depends on the concentration of a reactant

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38
Q

first order rxn

rate law

A

rate = k[A]1

k units = s-1

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39
Q

radioactive decay

A

first order reaction

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40
Q

radiocative decay eq

A

[A]t = [A]0e-kt

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41
Q

first order rxn graph

A

conc vs time: nonlinear

ln[A] vs time: k = -slope

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42
Q

second order reaction

A

nonconstant rate that depends on the concentration of a reactant

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43
Q

second order rxn rate law

A

rate = k[A]1[B]1 OR k[A]2

k units = 1/Ms

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44
Q

second order rxn graph

A

conc vs time: nonlinear

1/[A] vs time: slope = k

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45
Q

mixed order reactions

A

have a rate order that changes over time

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46
Q

broken order reactions

A

have noninteger orders

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47
Q

mixed order rxn eq

A
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48
Q

mixed order rxn

k3[A] >> k2

A

first order wrt A

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49
Q

mixed order rxn

k3[A] << k2

A

second order wrt A

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50
Q
A
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51
Q

What equation can be used to give us the rate of a reaction (in general)?

HINT: Rate = change in _______ / change in ________.

A

Rate = change in concentration / change in time

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52
Q

True or false? The Rate-Determining Step is able to control the rate of the overall reaction by acting as a kinetic bottleneck, preventing the speed of the reaction being faster than the slowest step involved.

A

True. The Rate-Determining Step is able to control the rate of the overall reaction by acting as a kinetic bottleneck, preventing the speed of the reaction being faster than the slowest step involved.

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53
Q

Which of the following would NOT determine the rate of a reaction?

(A) The energy of the reagents
(B) The orientation of the colliding molecules
(C) The size of the reagents
(D) How frequently the reagent molecules collide

A

(C) The size of the reagents

The 3 main factors determining a reaction rate are:

I. The energy of the reagents
II. The orientation of the colliding molecules
III. How frequently the reagent molecules collide

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54
Q

reversible reactions

A

eventually reach state in which energy is minimized and entropy is maximized

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55
Q

dynamic equilibrium

A

forward and reverse reactions are occurring at a constant rate

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56
Q

law of mass action

A

gives the expression for equilibrium constant, Keq, and the reaction quotient, Q,

pure solids and liquids do not appear

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57
Q

reaction quotient

A

Q

calculated value that relates the reactant and product concentrations at any given time during a reaction

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58
Q

Keq

A

ratio of products to reactants at equilibrium

constant at a constant temp

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59
Q

describe entropy and gibbs free energy at equlibrium

A

entropy is at a max

gibbs free energy is at a min

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60
Q

Q < Keq

A

more reactants than products

rxn proceeds in forward direction

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61
Q

Q = Keq

A

dynamic equilbrium

reactants = products

forward rate = reverse rate

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62
Q

Q > Keq

A

more products than reactants

reaction moves in reverse direction

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63
Q

the larger the value of Keq…

A

the farther to the right the equilibrium position

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64
Q

when Keq has large negative exponent

A

negligible

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65
Q

when see icebox

A

skip the box and go straight the the Keq eq

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66
Q

le chatliers principle

A

if stress is applied to a system, the system shifts to relieve that applied stress

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67
Q

three main types of stresses applied to a system:

A

changes in: concentration, pressure and volume, and temp

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68
Q

increasing the conc of reactants or decreasing the conc of products will shift the rxn…

A

to the right

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69
Q

increasing the conc of products or decreasing the conc of reactants will shift the rxn…

A

to the left

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70
Q

what happens to a systems volume and pressure when a system is compressed?

A

volume decreases and pressure increases

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71
Q

what happens to a system’s volume and pressure when a system is decompressed?

A

volume increases and pressure decreases

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72
Q

increasing the pressure of a gaseous system (dec its volume) will shift the system…

A

toward the side with fewer moles of gas

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73
Q

decreasing the pressure of a gaseous system (inc its volume) will shift the system…

A

toward the side with more moles of gas

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74
Q

increasing the temp an endothermic rxn will shift the rxn…

A

to the right

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75
Q

decreasing the temp of an exothermic rxn will shift the rxn…

A

to the right

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76
Q

decreasing the temp of an endothermic rxn will shift the rxn…

A

to the left

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77
Q

Increasing the temp of an exothermic rxn will shift the rxn…

A

to the left

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78
Q

if a rxn is endothermic, heat functions as a __reactant/product__

A

reactant

ΔH > 0

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79
Q

if a rxn is exothermic, heat functions as a __reactant/product__

A

product

ΔH < 0

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80
Q

kinetic products

A

higher in free energy than thermodynamic products

can form at lower temps

fast products

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81
Q

kinetic products can form at __lower/higher__ temps

A

lower

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82
Q

thermodynamic products

A

lower in free energy than kinetic products

more stable

slower

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83
Q

Some reactions are known as being Irreversible. Explain how Activation Energy would make a reaction Irreversible.

A

The Activation Energy for the forward reaction is low enough to be achievable in nature, whereas the backwards reaction must have such a high activation energy that this reaction is unlikely to occur.

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84
Q

e^(-Ea / RT) is also known as the f. F is equal to 3.74⋅10^-3. What does that tell you?

A

This means that for every 1,000 collisions, 3.74 collisions will result in a successful reaction. The higher the f, the higher the success rate of reactions.

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85
Q

Increasing the Activation Energy will ____________ the frequency of successful collisions. Increasing the Temperature will ____________ the frequency of successful collisions.

(A) Increase, Increase
(B) Increase, Decrease
(C) Decrease, Decrease
(D) Decrease, Increase
(D) Decrease, Increase

A

Increasing the Activation Energy will decrease the frequency of successful collisions. Increasing the Temperature will increase the frequency of successful collisions.

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86
Q

What is the difference between a unimolecular and bimolecular reaction?

A

In a unimolecular reaction, one molecule participates in the reaction: A -> products.

In a bimolecular reaction, two molecules participate in the reaction: A + B -> products.

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87
Q

True or False? You can write the rate law for one-step (elementary) reactions simply based on the reaction formula (A + B -> C).

A

True. You can write the rate law for one-step (elementary) reactions simply based on the reaction formula (A + B -> C). When dealing with multi-step reactions, however, you will need to determine the rate law experimentally.

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88
Q

True or False? The rate law for the overall reaction is equal to the rate law of the Rate-limiting Step.

A

True. The rate law for the overall reaction is equal to the rate law of the Rate-limiting Step.

89
Q

Activation Energy also plays a key factor in determining which of the 2 following types of products are formed?

(A) Stable and Instable
(B) Kinetic and Thermodynamic
(C) Rate-Determining and Rate-Limited
(D) None of the above

A

(B) Kinetic and Thermodynamic

Activation Energy plays a key role in determining if a reaction is under Kinetic or Thermodynamic Control, and which type of product is formed.

90
Q

What equation can be used to calculate ∆G based on Q?

A

∆G = ∆G° + RTlnQ

∆G = Gibb's Free Energy
∆G° = Standard Gibb's Free Energy
R = Gas Constant (8.314J/molK)
T = Temperature (298 K at standard conditions)
Q = Reaction Quotient
91
Q

Write the Keq expression for the following unbalanced reaction: O2 + N2H2 -> NO2 + H2

A
  • First, balance the reaction as follows:
    • 2O2 + N2H2 -> 2NO2 + H2
  • Then write the Keq expression as follows:
    • Keq = [NO2]^2[H2] / ([O2]^2[N2H2])
92
Q

What equation is used to calculate ∆G° based on the Equillibrium Constant?

A

∆G° = -RTlnK

∆G° = Standard Gibb's Free Energy
R = Gas Constant (8.314J/molK)
T = Temperature (298 K at standard conditions)
K = Equilibrium Constant
93
Q

When K = 1, what is the value of ∆G°? What about when K > 1? K < 1?

A

∆G° = 0 when K = 1.
∆G° > 0 when K < 1.
∆G° < 0 when K > 1.

94
Q

scientific method

A
  1. generate a hypothesis
    1. testable question
    2. gather data and resources
    3. form hypothesis
  2. test hypothesis
    1. collect new data
    2. analyze data
    3. interpret data and existing hypothesis
  3. publish and verify results
95
Q

hypothesis

A

proposed explanation or answer to testable question

often in form of if then statement

96
Q

finer method

A

assesses the value of a research question on the basis of whether or not it is feasible, interesting, novel, ethical, relevant

97
Q

basic science research

A

uses chemicals, cell cultures, or animal subjects

experiment based - good for demonstrating causality

98
Q

independent variable

A

manipulated variable

99
Q

dependent variable

A

measured or observed

100
Q

control

A

used to correct for any influences of an intervention that are not part of the model

101
Q

positive control

A

ensure that a change in the dependent variable occurs when expected

102
Q

negative control

A

ensure that no change in the dependent variable occurs when none is expected

103
Q

accuracy

(aka)

A

aka validity

ability to measure a true value

104
Q

precision

(aka)

A

aka reliability

ability to read consistently, or within a narrow range

105
Q

an inaccurate tool will introduce…

A

bias

106
Q

an imprecise tool will introduce…

A

error

107
Q

randomization

A

method used to control for differences between subject groups

108
Q

single blind experiments

A

only the patient or the assessor is blinded

109
Q

double blind experiment

A

investigator, subject, and assessor all do not know th subject’s group

110
Q

confounding

A

an error in data analysis that results from a common connection of both the dependent and independent variables to a third variable

111
Q

types of observational studies

A

cohort studies, cross sectional studies, case control studies

112
Q

cohort studies

A

record exposures throughout time and then assess the rate of a certain outcome

113
Q

cross sectional studies

A

assess both exposure and outcome at the same point in time

114
Q

case control studies

A

assess outcome status and then look backward to assess exposure history

115
Q

hill’s criteria

A

describe the components of an observed relationship that increase the likelihood of causality in the relationship

  1. temporality - necessary
  2. strength
  3. dose response relationship
  4. consistency
  5. plausibility
  6. consideration of alternative explanations
  7. experiment
  8. specificity
  9. coherence
116
Q

bias

A

systematic and results from a problem during data collection

117
Q

selection bias

A

sample not representative of the population

118
Q

detection bias

A

educated professionals use their knowledge in an inconsistent way by searching for an outcome disproportionately in certain populations

119
Q

Hawthorne effect

A

aka observation bias

changes in behavior, by the subject or experimenter or both, that occur as a result of the knowledge that the subject is being observed

120
Q

difference between bias and confounding

A

bias - systematic (unidirectional) error that occurs during data collection

confounding - error that occurs during data analysis

121
Q

4 principles of medical ethics

A

beneficence

nonmalificence

respect for patient autonomy

justice

122
Q

respect for persons

A

autonomy, informed consent, confidentiality

123
Q

justice

A

dictates which study questions are worth pursing and which subjects to use

124
Q

beneficence

A

requires use to do the most good wit the least harm

equipoise

125
Q

what is the difference between autonomy in medical ethics and respect for persons in research ethics?

A

autonomy: right of an indvidual to make decisions on their own behalf and to have those decisions be respected

respect for persons: honestly, confidentiality, informed consent, freedom from coercion

126
Q

what is the difference between a coercive influence and monetary compensation for a research study?

A

compensatory influence: does not impact the decision to participate

coercive influence: subject loses autonomy to make the decision to participate

127
Q

population

A

all of the individuals who share a set of charcteristics

128
Q

parameter

A

information that is calculated using every person in a population

129
Q

sample

A

subset of population

130
Q

statistics

A

sample data

131
Q

internal validity

A

identification of causality in a study between the independent and dependent variables

132
Q

external validity

A

genralizbility

133
Q

statistical significance

A

low likelihood of the experimental findings being due to chance

134
Q

clinical significance

A

usefulness or importance of experimental findings to patient care or patient outcomes

135
Q

why might small samples provide insufficient info about a population?

A

subject to more random variation than larger samples

in larger sample, outliers will have less of an effect on results

136
Q

what qualities must a study have to provide justification for an intervention?

A

statistical significance and clinical significance

137
Q

infrared (ir) sprectroscopy

A

measures absorption of infrared light, which causes molecular vibration (stretching, bending, twisting, and folding)

138
Q

wavenumber

A

used in IR spectroscopy

wavenumber = 1/λ

139
Q

how are IR spectra generally plotted?

A

percent transmittance vs wavenumber

140
Q

normal range of IR spectra

A

4000 - 400 cm-1

141
Q

fingerprint region of IR spectra

A

1500 - 400 cm-1

contains a number of peaks that can be used by experts to identify a compound

142
Q

why don’t symmetric stretches show up on IR spectra?

A

they involve no change in dipole movement

143
Q

IR spectra range

O-H

A

3000-3300 cm-1

broad/round

144
Q

IR spectra range

C=O

A

1750 cm-1

sharp

145
Q

IR spectra range

N-H

A

3300 cm-1

sharp

146
Q

3000-3300 cm-1

broad/round

A

IR spectra range

O-H

147
Q

1750 cm-1

sharp

A

IR spectra range

C=O

148
Q

3300 cm-1

sharp

A

IR spectra range

N-H

149
Q

percent transmittance

A

amount of light that passes through the sample and reaches the detector

150
Q

IR spectra range

O-H

carboxylic acid vs alcohol

A

alcohol: 3300 cm-1

carboxylic acid: 3000 cm-1

151
Q

what does IR spectroscopy measure?

A

measures absorption of IR light by specific bonds that vibrate

these vibrations cause changes in the dipole moment of the molecule that can be measured

152
Q

what does ultraviolet (UV) spectroscopy measure?

A

measures absorption of UV light, which causes the movement of electrons between molecular orbitals

153
Q

how are UV spectra obtained?

A

passing UV light through a sample that is usually dissolved in an inert, nonabsorbing solvent and recording the absorbance

154
Q

UV spectra

the more conjugated the compund… energy and wavelength

A

the lower the energy of the transition

the greater the wavelength of maximum absorbance

155
Q

what is UV spectroscropy useful for?

A

studying compounds containing double bodns or heteroatoms with lone pairs that create conjugated systems

156
Q

how are UV spectra generally plotted?

A

percent transmittance or absorbance vs wavelength

157
Q

what must a molecule have to appear on a UV spectrum?

A

small enough energy difference between its HOMO and LUMO to permit an electron to move from one orbital to the other

158
Q

UV spectra

the smaller the difference between the HOMO and LUMO, the ____ the wavelengths a molecule can abosrb

A

longer

159
Q

conjugation

A

occurs in molecules with unhybridized p-orbitals

can be excited by UV light

160
Q

how does conjugation affect the UV aborption spectrum?

A

shifts it -> higher max wavelengths (lower frequencies)

161
Q

what does nuclear magnetic resonance (NMR) spectroscropy measure?

A

measures alignment of nuclear spin with an applied magnetic field, which depends on the magnetic environment of the nucleus itself

162
Q

what is NMR useful for?

A

determining the structure (connectivity) of a compound, including functional groups

163
Q

how does NMR work?

A
  • based on fact that certain atomic nuclei have magnetic moments that are oriented at random
  • when nuclei are placed in a magnetic field, their magnetic moments tend to align either with or against the direction of the applied field
  • radiofrequency pulses push the nucleus from the alpha state to the beta state
    • these frequencies can be measured
164
Q

alpha state

A

lower energy

nuclei with magnetic moments

165
Q

beta state

A

higher energy

nuclei with magnetic moments

166
Q

magnetic resonance imaging (MRI)

A

medical application of NMR

reveals the relative density of specific types of protons

167
Q

how are NMR spectra generally plotted?

A

frequency vs absorption of energy

starndardized by using chemical shift

use TMS to calibrate

168
Q

TMS

A

has chemical shift of 0 ppm

169
Q

nuclei that have magnetic moments when placed in magnetic field

A

nuclei with odd mass numbers, odd atomic numbers, or both

170
Q

proton (1H) NMR

A

each unique group of protons has its own peak

171
Q

integration

A

proton NMR

area under the curve

proportional to the number of protons contained under the peak

172
Q

deshielding of protons

A

occurs when electron withdrawing groups pull electron density away from the nucleus, allowing it to be more easily affected y the magnetic field

moves a peak further downfield

173
Q

deshielding moves a peak ___field, to the __right/left__

A

downfield

left

174
Q

shielding moves a peak ___field, to the __right/left__

A

upfield

right

175
Q

shielding of protons

A

occurs when electron donating groups shield nuclei

moves a peak further upfield

176
Q

position of a peak in NMR is due to

A

shielding or deshielding effects

reflects the chemical environment of the protons

177
Q

NMR

splitting of the peak

A

represents the number of adjacent hydorgens

split into n + 1 subpeaks, where n is the number of adjacent hydrogens

178
Q

spin spin coupling (splitting)

A

when hydrogen are on adjacent atoms, they interfere with each other’s magnetic environment

include doublets, triplets, and multiplets

179
Q

n+1 rule

A

if a proton has n protons that are 3 bonds away, it will be split into n+1 pekas

(do not include protons attached to oxygen or nitrogen)

180
Q

what is proton NMR useful for?

A
  • determining the relative number of protons and their relative chemical environments
  • showing how many adjacent protons there are by splitting patterns
  • inferring certain functional groups
181
Q

how to approach NMR qs on MCAT

A

counting the number of peaks and unique hydrogens may be enough

(do not count the peak for TMS)

182
Q

NMR range

protons on sp3 hybridized carbons

A

0-3 ppm

183
Q

NMR range

protons on sp2 hybridized carbons

A

4.6-6 ppm

184
Q

NMR range

protons on sp hybridized carbosn

A

2-3 ppm

185
Q

NMR range

aldehyde hydrogens

A

9-10 ppm

186
Q

NMR range

carboxylic acid hydrogens

A

10.5-12 ppm

187
Q

NMR range

aromatic hydrogens

A

6-8.5 ppm

188
Q

0-3 ppm

A

NMR range

protons on sp3 hybridized carbons

189
Q

4.6-6 ppm

A

NMR range

protons on sp2 hybridized carbons

190
Q

2-3 ppm

A

NMR range

protons on sp hybridized carbosn

191
Q

9-10 ppm

A

NMR range

aldehyde hydrogens

192
Q

10.5-12 ppm

A

NMR range

carboxylic acid hydrogens

193
Q

6-8.5 ppm

A

NMR range

aromatic hydrogens

194
Q

True or false? The more densely the molecules are packed in the medium that light travels through, the faster the speed.

A

False. The more densely the molecules are packed in the medium that light travels through, the slower the speed.
This is why the speed of light in a vacuum is 3 x 10^8 m/s, whereas in Water, it is only 2.25 x 10^8 m/s!

195
Q

You produce a beautiful IR spectra and notice that there is 100 percent transmittance in some areas but not in others. What is happening in those areas that do not have 100 percent transmittance?

A

At that wavelength of light, 100 percent of the wave is not being transmitted through the compound because it is being absorbed by a bond causing it to stretch.

196
Q

Which of the following best describes the relationship between Transmittance and Absorbance?

(A) Transmittance + Absorbance = 100%
(B) Transmittance x Absorbance = 100%
(C) Transmittance / Absorbance = 100 %
(D) Transmittance - Absorbance = 100%

A

(A) Transmittance + Absorbance = 100%

This also means that 100%- (Transmittance) = Absorbance!

197
Q

Compare the Diagnostic Region and the Fingerprint Region of an IR Spectra.

A

The Diagnostic Region of an IR Spectra occurs above a wavenumber of 1500. It is useful for identifying which functional groups are present in a compound.

The Fingerprint Region of an IR Spectra occurs below a wavenumber of 1500. It is not especially useful for determining functional groups, but every compound has a unique fingerprint region, which can allow you to exactly identify a compound given the proper tools.

198
Q

Put the following in order of lowest wavenumber to highest wavenumber:

I. Csp3-H
II. Csp2-H
III. Csp-H

(A) I < II < III
(B) I < III < II
(C) III < II < I
(D) III < I < I

A

(A) I < II < III

In order of lowest wavenumber to highest wavenumber: Csp3-H < Csp2-H < Csp-H. This is due to increasing s character in the bonds.

199
Q

A given compound has 10 hydrogens. There are 4 peaks with integration values of 57.6, 11.3, 11.4, and 35.6. How many hydrogens are associated with the peak that has an integration value of 57.6?

(A) 3
(B) 4
(C) 5
(D) 6

A

(C) 5

I would notice that the lowest value is 11.3, which when divided by the total gives you a value close to .1; thus, I would know that this peak corresponds to 1/10th of the total hydrogens (10). Representing a single hydrogen. Because 57.6 is about 5 times larger, it must represent 5 hydrogens.

200
Q

What if you are given the integration values of 27.1, 40.1 and 40.9? What is the likely ratio of protons in each of the three groups?

(A) 1:2:2
(B) 2:3:3
(C) 3:4:4
(D) 27:40:41

A

(B) 2:3:3

Looking at this, I can round these numbers off to 27, 40.5 and 40.5, and I see that if you divide by a factor of 13.5, you can see a 2:3:3 ratio.
You could also try dividing 40.1 by 27.1, and get about 3/2.

201
Q

What is Splitting and when does it result? Describe what is the cause of Splitting.

A

Splitting is the splitting of a peak that occurs when you have nonequivalent protons next to each other. It is caused by the idea that the environment of a proton will be different when the neighboring proton is in its β versus α state.

202
Q

Match the number of peaks with the number of Hydrogens associated with each peak pattern, assuming there is splitting occurring.

I. Triplet
II. Doublet
III. Quintet

(A) 1
(B) 2
(C) 3
(D) 4

A

I. Triplet (B) 2

II. Doublet (A) I

III. Quintet (D) 4

203
Q

True or false? If you see a singlet, there cannot be any splitting of that Hydrogen.

A

True. If you see a singlet, there cannot be any splitting of that Hydrogen.

204
Q

Which of the following compounds could appear on an NMR?

I. C-14
II. O-15
III. S-32

(A) I only
(B) II only
(C) I and III only
(D) I, II and III

A

(B) II only

To appear on an NMR, an atom must have an odd mass number, an odd atomic number, or both. Only O-15 meets either of these criteria.

205
Q

Based on the previous description of what makes molecules sensitive to NMR, what is the Carbon Isotope used for Carbon NMR?

A

Carbon-13, since it has an odd mass number.

206
Q

Fill in the blanks: Because a double bond is ______________ than a single bond, it requires (a) ______________ to vibrate the bond, which means there is ___________ energy needed to cause that vibration.

(A) Longer, more force, more
(B) Stiffer, less force, less
(C) Stiffer, higher wavenumber, more
(D) More elastic, lower wavenumber, less

A

(C) Stiffer, higher wavenumber, more

Because a double bond is Stiffer than a single bond, it requires a higher wavenumber to vibrate the bond, which means there is More energy needed to cause that vibration.

207
Q

CRB True or false? If the Hydrogen in the Carboxylic Acid were replaced by Tritium (Hydrogen with an atomic mass of 3), then the O-T bond would have a higher wavenumber than the original O-H bond.

A

False. If the Hydrogen in the Carboxylic Acid were replaced by Tritium (Hydrogen with an atomic mass of 3), then the O-T bond would have a lower wavenumber than the original O-H bond.

This is because a more massive atom will vibrate more slowly and at lower frequencies.

208
Q

CRB Kyrie is having a tough time remembering that a heavier atom will have a lower stretching frequency (wavenumber). Can you think of an easier to remember example?

A

The easiest way to remember this is by comparing C-H and C-C bonds. C-H bonds have a wavenumber near 3000 cm^-1, whereas C-C bonds are in the fingerprint region below1500 cm^-1.

209
Q

Since having a heavier atom leads to a lower wavenumber, what type of relationship do atomic weight and wavenumbers have?

(A) Linear
(B) Positive Correlation
(C) Exponential
(D) Negative Correlation

A

(D) Negative Correlation

Since an increase in one factor leads to a decrease in the other, this is a negative correlation.

210
Q

Since a stiffer bond leads to a higher wavenumber, what type of relationship do wavenumbers and bond stiffness have?

(A) Linear
(B) Positive Correlation
(C) Exponential
(D) Negative Correlation

A

(B) Positive Correlation

Since an increase in one will lead to an increase in the other, this is a positive correlation.

211
Q

CRB True or false? A more conjugated compound will be even more stable, so it will need more energy (shorter wavelengths) to be excited than less conjugated compounds.

A

False. A more conjugated compound will be more stable than less conjugated systems if one electron pair is excited above ground state, so it can use less energy (longer wavelengths) to be excited.

212
Q

A certain compound has a peak on an IR-Spectrum around 530 nm (green). What color do you expect this compound to be?

A

You’d expect the compound to be red since it’s complimentary color, green, is what is being absorbed.

213
Q

Thus, what is the relationship between wavelength and conjugation? How does this relate to color?

A

The greater the conjugation, the higher the wavelength. The higher the wavelength, the less likely for the wavelength to be UV light and more likely to be in the visible light spectrum.

214
Q

A Proton can be viewed as a tiny magnet, which means it has a magnetic field. You are looking down on a proton and notice that it is spinning in a counter-clockwise direction. In which direction does the magnetic field point?

(A) Counter-clockwise
(B) Clockwise
(C) Away from you
(D) Towards you

A

(D) Towards you

This can be determined using the right-hand rule.

215
Q

Proton A is more deshielded than Proton B. Which proton will appear farther downfield in an NMR Spectra?

(A) Proton A because going from the α to the β state will take more energy than with Proton B.
(B) Proton A because going from the α to the β state will take less energy than with Proton B.
(C) Proton B because going from the α to the β state will take more energy than with Proton A.
(D) Proton B because going from the α to the β state will take less energy than with Proton A.

A

(A) Proton A because going from the α to the β state will take more energy than with Proton B.

Proton A is more deshielded, resulting in a greater βeff, which results in a greater energy difference between the α and the β state, which results in a greater energy required. Greater energy corresponds to a higher frequency, which is farther downfield in an NMR Spectra.

216
Q

When speaking about NMR, what does it mean to say that protons are “chemically equivalent”? How does this relate to how they will appear in an NMR Spectra?

A

To say that protons are “chemically equivalent” is to say that the protons are in the same magnetic environment. These protons will therefore correspond to the same, single peak in an IR Spectra.

217
Q

How many signals would you expect to result from propane on an NMR Spectra?

(A) 1
(B) 2
(C) 3
(D) 4

A

(B) 2

Propane has 8 protons total, with 2 being in one magnetic environment and 6 being in another. Because there are two magnetic environments, propane will display two peaks in an NMR Spectra.

218
Q

How many signals would you expect to result from 1-propanol on an NMR Spectra?

(A) 1
(B) 2
(C) 3
(D) 4

A

(D) 4

1-Propanol has 8 total protons in four different environments: 2 on carbon 1, 2 on carbon 2, 3 on carbon 3, and the final one bound to the oxygen. Because there are 4 magnetic environments, propanol will display 4 peaks on an NMR spectra.

219
Q

Use hybridization to explain why alkenes are more deshielded than alkanes.

A

Alkenes are sp2-hybridized, giving them more s character than the sp3-hybridized orbitals of alkanes. sp2 orbitals have greater s-character and correspond with being closer to the nucleus and having greater electron density, which would result in greater deshielding of a nearby proton.

MCAT (26 decks)

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