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MCAT > MCAT Organic Chemistry > Flashcards

MCAT Organic Chemistry Flashcards

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MCAT flashcards
1
Q

A destabilizing interaction between substituents that occupy axial positions on the same side of a cyclohexane ring

A

1,3-diaxial interaction

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2
Q

Epimers formed by ring closure

A

Anomers

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3
Q

The most stable conformation of cyclohexanes

A

chair conformation

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4
Q

Any compounds that have the same molecular formula and the same connectivity but that differ from one another by rotation about a sigma bond

A

Conformational isomers

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5
Q

Any compounds with the same molecular formula but whose atoms have different connectivity

A

Constitutional isomers

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6
Q

Molecules that are mirror images and non-superimposable

A

Enantiomers

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7
Q

Diasteromers that differ in configuration at only one of many chiral centers

A

Epimers

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8
Q

Diastereomers that differ in orientation of sibstituents around a ring or double bond

A

Geometric isomers

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9
Q

A molecule that contains chiral centers and an internal plane of symmetry

A

Meso

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10
Q

Any compound with the same molecular formula and connectivity that differ only in the spatial arrangement of atoms, are known as stereoisomers. Note that if the compounds only differ by rotation around a sigma bond they are not stereoisomers but confirmational isomers

A

Stereoisomers

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11
Q

A purification method based on a difference in boiling points

A

Distillation

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12
Q

A separation technique that relies on relative solubilities of the two solvents used

A

Extraction

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13
Q

A method that detects the vibration of covalent bonds and can differentiate their frequencies, which is related to the type of bond

A

Infrared spectroscopy

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14
Q

A rapid technique used to separate compounds based on their polarity

A

Thin-layer chromatography (TLC)

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15
Q

Forces between temporary dipoles formed in nonpolar molecules because of a temporary asymmetric electron distribution

A

van der Waals Forces

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16
Q

not forming a homogeneous mixture when added together.

A

Immiscible

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17
Q

Why is it best to use a 5% sodium bicarbonate solvent when trying to extract carboxylic acids?

A

A solvent of dilute sodium hydroxide could do it, but it would also convert phenols into their anionic salts

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18
Q

What would you use to extract phenols in an extraction technique?

A

I would use 10% sodium hydroxide to convert phenols into their corresponding anionic salts

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19
Q

In thin layer chromatography, compounds are separated based on differing___

A

polarities

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20
Q

In TLC, the more polar components of the mixture interact more with the polar stationary phase, and travel at a __

A

slower rate

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21
Q

In TLC, the less polar components have a greater affinity for the solvent than the stationary phase, and travel with the mobile solvent __

A

at a faster rate than the more polar components

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22
Q

What is the Rf value in TLC

A

It is the distance traveled by an individual component divided by the distance traveled by the mobile solvent

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23
Q

What is TLC good for doing?

A

TLC is a good technique for separating very small amounts of material in order to assess how many compounds make up a micture

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24
Q

When would you use column (flash) chromatography over thin-layer chromatography?

A

It is best to use flash chromatography to isolate bulk compounds

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25
Q

In flash chromatography, the more polar compound will___

A

spend more time adsorbed on the polar solid phase, travel slowly down the column than nonpolar compounds

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26
Q

Compounds in flash chromatography can be expected to leave the column ___

A

in order of polarity (least polar compounds first, then most polar compounds)

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27
Q

When would you use ion exchange chromatography?

A

When the materials being separated have varying charge states

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28
Q

____is frequently used in the separation of mixtures of proteins

A

Ion exchange chromatography

29
Q

In a cation exchange resin, ion exchange chromatography, proteins with pI values greater than the pH of the mobile phase ___

A

will be positively charged and elute slowly compared to those with pI values below the solution pH

30
Q

In an anion exchange resin, proteins with pI values above the pH of the solution___

A

will elute first

31
Q

Why is the speed and efficiency if High Performance Liquid Chromatography more than column chromatography

A

The mobile phase is forced through the stationary phase at very high pressure, both the speed and efficiency of the separation is increased, it is an improvement over column chromatography

32
Q

In HPLC, _____ elute first

A

More polar compounds elute first in HPLC as they have a higher affinity for the mobile phase

33
Q

Why do nonpolar compounds elute slower from HPLC?

A

They interact longer with the nonpolar stationary phase, they elute last

34
Q

___is a techinque used to separate bulk materials based on molecular size

A

Size Exclusion Chromatography

35
Q

In size exlusion chromatography which sort of molecules elute faster and why?

A

Size exlusion chromatography uses chemically inert porous polymer beads, that allow permeation of small molecules through them, larger molecules move down by the interparticle pathway, smaller particles go down by the intraparticle pathway. The larger particles have a more direct pathway and elute faster

36
Q

___ is used for the separation of full proteins from smaller peptide chains

A

Size exclusion chromatography, HOWEVER the technique is not effective when separating two compounds that are similar in size

37
Q

___ is most commonly used to purify proteins or nucleic acids from complex biochemical mixtures like cell lysates, growth media, or blood, rather than a reaction mixture

A

Affinity chromatography

38
Q

___ is a separation technique that takes place between the mobile gas phase and a stationary liquid phase

A

Gas chromatography

39
Q

The separation of compounds in a mixture using gas chromatography is based on their __

A

different volatilities

40
Q

In Gas chromatography, if the interactions of the substrates with the column are similar, the more volatile components emerge from the column__

A

the more volatile components emerge from the column first, and the less volatile components emerge from the column later

41
Q

Branching tends to __

A

inhibit van der Waals forces by reducing the surface area available for intermolecular interactions

42
Q

___is the process of raising the temperature of a liquid until it can overcome the intermolecular forces that hold it together in the liquid phase

A

Distillations

43
Q

___is performed when trace impurities need to be removed fro ma relatively pure compound, OR when a mixture of compounds with significantly different boiling points need to be separated

A

Simple distillation

44
Q

Fractional distillation is used when __

A

the difference in boiling points of the components in the liquid mixture are not that large

45
Q

How does absorption spectoscopy work?

A

Molecules are exposed to various forms of light, exciting the molecules to a higher energy state, then when energy is released as their relax back to ground state the measured energy can reveal structural features of the molecules in the sample

46
Q

___allows researchers to determine the mass of compounds in a sample

A

Mass spectrometry

47
Q

What occurs in the mass spectrometer?

A

Molecules are ionized in a high vacuum by bombarding them with high energy electrons, then they enter region of spectrometer where they are acted on by a magnetic field that causes a change in flight path based off the mass of the ion.

48
Q

On a mass spectrometer, bromine will appear as ___

A

79 amu or 81 amu nearly equal in height

49
Q

On a mass spectrometer chlorine will occur in two isotopes at ___

A

35 amu (75% abundance) and 37 amu (25% abundance)

50
Q

Mass spectra for chlorinated molecules will have __

A

a peak 2 amu heavier than the main peak and about one-third its height

51
Q

What kind of molecules are ultraviolet/visible spectroscopy used for?

A

It is very useful in monitoring complexes of transition metals in the closely spaced d-orbitals

-MAINLY : it is used to study highly conjugated organic systems

52
Q

Describe how conjugation affects ultraviolet and visible spectroscopy

A

The wavelength of maximum absorption for any compound is directly related to the extent of cinjugation in the molecule, the more extensive the conjugated system is, the LONGER the wavelength of maximum absorption will be

53
Q

The color a compound maximally absorbs is __

A

complementary to the color it will appear to our eyes
Example: IF i absorb BLUE i appear ORANGE
If i absorb RED I appear GREEN
If I absorb Yellow I appear VIOLET

54
Q

On IR spectroscopy a very strong and sharp peak at 1700 cm-1 is a

A

Carbonyl group

C=O

55
Q

On IR spectroscopy, Alkenes are centered around _____

A

1650 cm-1

56
Q

If you don’t see a carbonyl group in IR spectroscope, you can eliminate a bunch of functional groups such as

A

aldehydes, ketones, carboxyic acids, acid chlorides, esters, amides, anhydrides

57
Q

A triple bond on IR spectroscopy will appear between

A

2260-2100 cm-1

58
Q

Why is there broadness in the O-H stretch on IR spectroscopy?

A

The broadness is due to the hydrogen bonding

59
Q

The O-H stretch on IR spectroscopy can be found around ___

A

3600-3200 cm-1

60
Q

The C-H stretch for sp3 carbons on IR spectroscopy is

A

3000-2850 cm-1

61
Q

The C-H stretch for sp2 carbons on IR spectroscopy is __

A

3150-3000 cm-1

62
Q

The C-H stretch for sp carbons on IR spectroscopy is __

A

3300 cm-1

63
Q

In all types of NMR spectroscopy light from the __ of the electromagnetic spectrum is used to induce energy absorption

A

Radio frequency range

64
Q

Equivalent hydrogens in H NMR are those that__

A

have identical electronic environments. They are considered equivalent if they can be interchanged by a free rotation or a symmetry operation (mirror plane or rotational axis)

65
Q

A set of protons near an electronegative group is to be ___ and will appear ___ in the H NMR spectrum

A

deshielded and will appear DOWNFIELD (to the LEFT)

66
Q

3 factors involed in proton shielding are

A
  1. electronegativity of the neighboring atoms
  2. hybridization
  3. acidity and hydrogen bonding
67
Q

The greater the s-character, the more ___

A

deshielded the set of protons is and will appear DOWNFIELD (left)

68
Q

An aromatic proton on an H NMR will appear around

A

6.5-8 ppm

69
Q

an alkene proton will appear on an H NMR around

A

5-6 ppm

MCAT (45 decks)

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