Physics II: 4-6, 9-10 Flashcards
chemical mechanisms
propose a series of steps that make up the overall reaction
intermediates
molecules that exist within the course of a reaction but are neither reactants nor products overall
rate determining step
slowest step
limits the maximum rate at which a reaction can proceed
collision theory
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)
collision theory
for a collision to be effective…
molecules must be in the proper orientation and have sufficient kinetic energy to exceed the activation energy
activation energy
Ea
minimum energy of collision necessary for a reaction to take place
collision theory eq
rate = Z x f
Z = total number of collisions occurring per second
f = fraction of collisions that are effective
arrhenius eq
A = frequency actor
R = ideal gas constant
frequency factor
A
aka attempt frequency
measure of how often molecules in a certain reaction collide
Arrhenius eq
relationship between freq factor and rate constant
direct relationship
as freq factor inc, rate constant inc
arrhenius eq
exponent relationship
as the exponent gets smaller, it becomes less negative -> increases create constant
arrhenius eq
what makes the negative exponent smaller? what does this do?
low activation energy and high temp -> inc rate constant
how to increase frequency factor
increase number of molecules in a vessel (opportunities for collision are increased)
transition state theory
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
transition state
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
free energy change of the reaction
ΔGrxn
difference between the free energy of the products and the free energy of the reactants
exergonic reaction
-ΔG
energy is given off
endergonic reaction
+ΔG
energy is absorbed
exergonic reaction diagram
endergonic reaction diagram
how do reaction concentrations affect reaction rate?
conc of reactants inc, number of effective collisions inc (frequency factor)
reaction rate will increase for all but zero order reactions
how does temperature affect reaction rate?
reaction rate inc, temp inc
bc temp is measure of particles’ avg kinetic energy
optimal temp for enzymatic reaction
35 - 40 C
how does the medium in which rxn takes place affect reaction rate?
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
how do catalysts affect reaction rate?
increase reaction rate without being consumed in the rxn
lowers activation energy for both forward and backward rxn
catalysts
increase reaction rate without being consumed in rxn
stabilize reactants so as to reduce the activation energy necessary for the rxn to proceed
homogenous catalysis
catalyst is in same phase as reactants
heterogeneous catalysis
catalyst is in a different phase from reactants
what do catalysts not affect?
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
how are rate laws determined?
experimentally
rate law eq
rate = k[A]x[B]y
aA + bB -> cC + dD
eq to determine the order of reactant A experimentally
Δrate = Δ[A]x
multiplication factors
zero order reaction
rate of formation of product C is independent of change sin concentrations of any of the reactants
zero order reaction
rate law
rate = k[A]0[B]0 = k
k units: M/s
ways to change the rate of zero order rxn
change temperature, add catalyst
zero order rxn graph
slope
conc vs time: linear, k = -slope
first order rxn
have a nonconstant rate that depends on the concentration of a reactant
first order rxn
rate law
rate = k[A]1
k units = s-1
radioactive decay
first order reaction
radiocative decay eq
[A]t = [A]0e-kt
first order rxn graph
conc vs time: nonlinear
ln[A] vs time: k = -slope
second order reaction
nonconstant rate that depends on the concentration of a reactant
second order rxn rate law
rate = k[A]1[B]1 OR k[A]2
k units = 1/Ms
second order rxn graph
conc vs time: nonlinear
1/[A] vs time: slope = k
mixed order reactions
have a rate order that changes over time
broken order reactions
have noninteger orders
mixed order rxn eq
mixed order rxn
k3[A] >> k2
first order wrt A
mixed order rxn
k3[A] << k2
second order wrt A
What equation can be used to give us the rate of a reaction (in general)?
HINT: Rate = change in _______ / change in ________.
Rate = change in concentration / change in time
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.
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.
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
(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
reversible reactions
eventually reach state in which energy is minimized and entropy is maximized
dynamic equilibrium
forward and reverse reactions are occurring at a constant rate
law of mass action
gives the expression for equilibrium constant, Keq, and the reaction quotient, Q,
pure solids and liquids do not appear
reaction quotient
Q
calculated value that relates the reactant and product concentrations at any given time during a reaction
Keq
ratio of products to reactants at equilibrium
constant at a constant temp
describe entropy and gibbs free energy at equlibrium
entropy is at a max
gibbs free energy is at a min
Q < Keq
more reactants than products
rxn proceeds in forward direction
Q = Keq
dynamic equilbrium
reactants = products
forward rate = reverse rate
Q > Keq
more products than reactants
reaction moves in reverse direction
the larger the value of Keq…
the farther to the right the equilibrium position
when Keq has large negative exponent
negligible
when see icebox
skip the box and go straight the the Keq eq
le chatliers principle
if stress is applied to a system, the system shifts to relieve that applied stress
three main types of stresses applied to a system:
changes in: concentration, pressure and volume, and temp
increasing the conc of reactants or decreasing the conc of products will shift the rxn…
to the right
increasing the conc of products or decreasing the conc of reactants will shift the rxn…
to the left
what happens to a systems volume and pressure when a system is compressed?
volume decreases and pressure increases
what happens to a system’s volume and pressure when a system is decompressed?
volume increases and pressure decreases
increasing the pressure of a gaseous system (dec its volume) will shift the system…
toward the side with fewer moles of gas
decreasing the pressure of a gaseous system (inc its volume) will shift the system…
toward the side with more moles of gas
increasing the temp an endothermic rxn will shift the rxn…
to the right
decreasing the temp of an exothermic rxn will shift the rxn…
to the right
decreasing the temp of an endothermic rxn will shift the rxn…
to the left
Increasing the temp of an exothermic rxn will shift the rxn…
to the left
if a rxn is endothermic, heat functions as a __reactant/product__
reactant
ΔH > 0
if a rxn is exothermic, heat functions as a __reactant/product__
product
ΔH < 0
kinetic products
higher in free energy than thermodynamic products
can form at lower temps
fast products
kinetic products can form at __lower/higher__ temps
lower
thermodynamic products
lower in free energy than kinetic products
more stable
slower
Some reactions are known as being Irreversible. Explain how Activation Energy would make a reaction Irreversible.
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.
e^(-Ea / RT) is also known as the f. F is equal to 3.74⋅10^-3. What does that tell you?
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.
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
Increasing the Activation Energy will decrease the frequency of successful collisions. Increasing the Temperature will increase the frequency of successful collisions.
What is the difference between a unimolecular and bimolecular reaction?
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.
True or False? You can write the rate law for one-step (elementary) reactions simply based on the reaction formula (A + B -> C).
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.
True or False? The rate law for the overall reaction is equal to the rate law of the Rate-limiting Step.
True. The rate law for the overall reaction is equal to the rate law of the Rate-limiting Step.
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
(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.
What equation can be used to calculate ∆G based on Q?
∆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
Write the Keq expression for the following unbalanced reaction: O2 + N2H2 -> NO2 + H2
- First, balance the reaction as follows:
- 2O2 + N2H2 -> 2NO2 + H2
- Then write the Keq expression as follows:
- Keq = [NO2]^2[H2] / ([O2]^2[N2H2])
What equation is used to calculate ∆G° based on the Equillibrium Constant?
∆G° = -RTlnK
∆G° = Standard Gibb's Free Energy R = Gas Constant (8.314J/molK) T = Temperature (298 K at standard conditions) K = Equilibrium Constant
When K = 1, what is the value of ∆G°? What about when K > 1? K < 1?
∆G° = 0 when K = 1.
∆G° > 0 when K < 1.
∆G° < 0 when K > 1.
scientific method
- generate a hypothesis
- testable question
- gather data and resources
- form hypothesis
- test hypothesis
- collect new data
- analyze data
- interpret data and existing hypothesis
- publish and verify results
hypothesis
proposed explanation or answer to testable question
often in form of if then statement
finer method
assesses the value of a research question on the basis of whether or not it is feasible, interesting, novel, ethical, relevant
basic science research
uses chemicals, cell cultures, or animal subjects
experiment based - good for demonstrating causality
independent variable
manipulated variable
dependent variable
measured or observed
control
used to correct for any influences of an intervention that are not part of the model
positive control
ensure that a change in the dependent variable occurs when expected
negative control
ensure that no change in the dependent variable occurs when none is expected
accuracy
(aka)
aka validity
ability to measure a true value
precision
(aka)
aka reliability
ability to read consistently, or within a narrow range
an inaccurate tool will introduce…
bias
an imprecise tool will introduce…
error
randomization
method used to control for differences between subject groups
single blind experiments
only the patient or the assessor is blinded
double blind experiment
investigator, subject, and assessor all do not know th subject’s group
confounding
an error in data analysis that results from a common connection of both the dependent and independent variables to a third variable
types of observational studies
cohort studies, cross sectional studies, case control studies
cohort studies
record exposures throughout time and then assess the rate of a certain outcome
cross sectional studies
assess both exposure and outcome at the same point in time
case control studies
assess outcome status and then look backward to assess exposure history
hill’s criteria
describe the components of an observed relationship that increase the likelihood of causality in the relationship
- temporality - necessary
- strength
- dose response relationship
- consistency
- plausibility
- consideration of alternative explanations
- experiment
- specificity
- coherence
bias
systematic and results from a problem during data collection
selection bias
sample not representative of the population
detection bias
educated professionals use their knowledge in an inconsistent way by searching for an outcome disproportionately in certain populations
Hawthorne effect
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
difference between bias and confounding
bias - systematic (unidirectional) error that occurs during data collection
confounding - error that occurs during data analysis
4 principles of medical ethics
beneficence
nonmalificence
respect for patient autonomy
justice
respect for persons
autonomy, informed consent, confidentiality
justice
dictates which study questions are worth pursing and which subjects to use
beneficence
requires use to do the most good wit the least harm
equipoise
what is the difference between autonomy in medical ethics and respect for persons in research ethics?
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
what is the difference between a coercive influence and monetary compensation for a research study?
compensatory influence: does not impact the decision to participate
coercive influence: subject loses autonomy to make the decision to participate
population
all of the individuals who share a set of charcteristics
parameter
information that is calculated using every person in a population
sample
subset of population
statistics
sample data
internal validity
identification of causality in a study between the independent and dependent variables
external validity
genralizbility
statistical significance
low likelihood of the experimental findings being due to chance
clinical significance
usefulness or importance of experimental findings to patient care or patient outcomes
why might small samples provide insufficient info about a population?
subject to more random variation than larger samples
in larger sample, outliers will have less of an effect on results
what qualities must a study have to provide justification for an intervention?
statistical significance and clinical significance
infrared (ir) sprectroscopy
measures absorption of infrared light, which causes molecular vibration (stretching, bending, twisting, and folding)
wavenumber
used in IR spectroscopy
wavenumber = 1/λ
how are IR spectra generally plotted?
percent transmittance vs wavenumber
normal range of IR spectra
4000 - 400 cm-1
fingerprint region of IR spectra
1500 - 400 cm-1
contains a number of peaks that can be used by experts to identify a compound
why don’t symmetric stretches show up on IR spectra?
they involve no change in dipole movement
IR spectra range
O-H
3000-3300 cm-1
broad/round
IR spectra range
C=O
1750 cm-1
sharp
IR spectra range
N-H
3300 cm-1
sharp
3000-3300 cm-1
broad/round
IR spectra range
O-H
1750 cm-1
sharp
IR spectra range
C=O
3300 cm-1
sharp
IR spectra range
N-H
percent transmittance
amount of light that passes through the sample and reaches the detector
IR spectra range
O-H
carboxylic acid vs alcohol
alcohol: 3300 cm-1
carboxylic acid: 3000 cm-1
what does IR spectroscopy measure?
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
what does ultraviolet (UV) spectroscopy measure?
measures absorption of UV light, which causes the movement of electrons between molecular orbitals
how are UV spectra obtained?
passing UV light through a sample that is usually dissolved in an inert, nonabsorbing solvent and recording the absorbance
UV spectra
the more conjugated the compund… energy and wavelength
the lower the energy of the transition
the greater the wavelength of maximum absorbance
what is UV spectroscropy useful for?
studying compounds containing double bodns or heteroatoms with lone pairs that create conjugated systems
how are UV spectra generally plotted?
percent transmittance or absorbance vs wavelength
what must a molecule have to appear on a UV spectrum?
small enough energy difference between its HOMO and LUMO to permit an electron to move from one orbital to the other
UV spectra
the smaller the difference between the HOMO and LUMO, the ____ the wavelengths a molecule can abosrb
longer
conjugation
occurs in molecules with unhybridized p-orbitals
can be excited by UV light
how does conjugation affect the UV aborption spectrum?
shifts it -> higher max wavelengths (lower frequencies)
what does nuclear magnetic resonance (NMR) spectroscropy measure?
measures alignment of nuclear spin with an applied magnetic field, which depends on the magnetic environment of the nucleus itself
what is NMR useful for?
determining the structure (connectivity) of a compound, including functional groups
how does NMR work?
- 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
alpha state
lower energy
nuclei with magnetic moments
beta state
higher energy
nuclei with magnetic moments
magnetic resonance imaging (MRI)
medical application of NMR
reveals the relative density of specific types of protons
how are NMR spectra generally plotted?
frequency vs absorption of energy
starndardized by using chemical shift
use TMS to calibrate
TMS
has chemical shift of 0 ppm
nuclei that have magnetic moments when placed in magnetic field
nuclei with odd mass numbers, odd atomic numbers, or both
proton (1H) NMR
each unique group of protons has its own peak
integration
proton NMR
area under the curve
proportional to the number of protons contained under the peak
deshielding of protons
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
deshielding moves a peak ___field, to the __right/left__
downfield
left
shielding moves a peak ___field, to the __right/left__
upfield
right
shielding of protons
occurs when electron donating groups shield nuclei
moves a peak further upfield
position of a peak in NMR is due to
shielding or deshielding effects
reflects the chemical environment of the protons
NMR
splitting of the peak
represents the number of adjacent hydorgens
split into n + 1 subpeaks, where n is the number of adjacent hydrogens
spin spin coupling (splitting)
when hydrogen are on adjacent atoms, they interfere with each other’s magnetic environment
include doublets, triplets, and multiplets
n+1 rule
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)
what is proton NMR useful for?
- 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
how to approach NMR qs on MCAT
counting the number of peaks and unique hydrogens may be enough
(do not count the peak for TMS)
NMR range
protons on sp3 hybridized carbons
0-3 ppm
NMR range
protons on sp2 hybridized carbons
4.6-6 ppm
NMR range
protons on sp hybridized carbosn
2-3 ppm
NMR range
aldehyde hydrogens
9-10 ppm
NMR range
carboxylic acid hydrogens
10.5-12 ppm
NMR range
aromatic hydrogens
6-8.5 ppm
0-3 ppm
NMR range
protons on sp3 hybridized carbons
4.6-6 ppm
NMR range
protons on sp2 hybridized carbons
2-3 ppm
NMR range
protons on sp hybridized carbosn
9-10 ppm
NMR range
aldehyde hydrogens
10.5-12 ppm
NMR range
carboxylic acid hydrogens
6-8.5 ppm
NMR range
aromatic hydrogens
True or false? The more densely the molecules are packed in the medium that light travels through, the faster the speed.
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!
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?
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.
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) Transmittance + Absorbance = 100%
This also means that 100%- (Transmittance) = Absorbance!
Compare the Diagnostic Region and the Fingerprint Region of an IR Spectra.
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.
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) 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.
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
(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.
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
(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.
What is Splitting and when does it result? Describe what is the cause of Splitting.
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.
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
I. Triplet (B) 2
II. Doublet (A) I
III. Quintet (D) 4
True or false? If you see a singlet, there cannot be any splitting of that Hydrogen.
True. If you see a singlet, there cannot be any splitting of that Hydrogen.
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
(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.
Based on the previous description of what makes molecules sensitive to NMR, what is the Carbon Isotope used for Carbon NMR?
Carbon-13, since it has an odd mass number.
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
(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.
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.
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.
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?
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.
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
(D) Negative Correlation
Since an increase in one factor leads to a decrease in the other, this is a negative correlation.
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
(B) Positive Correlation
Since an increase in one will lead to an increase in the other, this is a positive correlation.
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.
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.
A certain compound has a peak on an IR-Spectrum around 530 nm (green). What color do you expect this compound to be?
You’d expect the compound to be red since it’s complimentary color, green, is what is being absorbed.
Thus, what is the relationship between wavelength and conjugation? How does this relate to color?
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.
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
(D) Towards you
This can be determined using the right-hand rule.
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) 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.
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?
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.
How many signals would you expect to result from propane on an NMR Spectra?
(A) 1
(B) 2
(C) 3
(D) 4
(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.
How many signals would you expect to result from 1-propanol on an NMR Spectra?
(A) 1
(B) 2
(C) 3
(D) 4
(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.
Use hybridization to explain why alkenes are more deshielded than alkanes.
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.
