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MCAT Organic Chemistry > 1. Molecular Structure > Flashcards

1. Molecular Structure Flashcards

1
Q

sigma bond

A

single bond. The electrons are localized DIRECTLY BETWEEN the two bonding atoms. They have the lowest energy and is the most stable of covalent bond.

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2
Q

pi bond

A

forms the 2nd bond in double bond (above below atoms) and 2nd and 3rd bond in triple bond (above/below and on two sides of atoms). Uses p-orbitals. Weaker than sigma bonds, but increases bond strenght over all. Bond length decreases.

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3
Q

Absolute Configuration

A

Method to describe chiral centers. R - right, S - left.

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4
Q

Anomeric Carbon

A

The carbon of the anomer. Glucose: ALPHA when OH is DOWN; BETA when OH is UP.

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5
Q

Anomers

A

If a ring closure occurs at the epimeric carbon (chiral carbon of 2 diastereomers), two possible diastereomers are formed.

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6
Q

Aromatic

A

Has resonance and comply to Huckel’s Rule of 4n+2 pie electrons.

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7
Q

Ball and Stick Models

A

Show atomic radius of atoms to scale. Bond lengths not to scale.

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8
Q

Bond-Line Formula

A

Corners, ending of lines represent carbons. Hydrogens are not shown. Other functional groups are written in.

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9
Q

Character

A

Resembling shape and energy of the s and p orbitals that form it.

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10
Q

Chiral Character

A

Mirror images. Non-superimposable. Carbon is only chiral when it has FOUR DIFFERENT substituents.

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11
Q

Cis-isomers

A

A geometric isomer with substituents on the same side. Has dipole moment. Cis have STRONGER intermolecular forces leading to HIGHER boiling points, due to LOWER symmetry, cis molecules CANNOT form crystals readily, has LOWER melting points. Written as Z before molecular’s name describing higher priority group is on the zame zide.

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12
Q

Condensed Formula

A

Doesn’t show bonding.

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13
Q

Configuration

A

Absolute configuration (R and S) and Relative configuration (substituents connectivity)

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14
Q

Conformational Isomers

A

aka conformers.

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15
Q

Conformers

A

Not true isomers. Different spatial orientations of the same molecule. Such as molecule rotating about it’s single bond.

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16
Q

Coordinate Covalent Bond

A

This is where one nucleus can donate both electrons instead of one electron from each nucleus.

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17
Q

Dash Formula

A

Shows bonding, but not 3D structure.

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18
Q

Dash-Line-Wedge Formula

A

Wedge is coming out of the page. Dash is going into the page. Lines are in the plane.

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19
Q

Degree of Unsaturation

A

Formula = (2C + 2 + N - X - H)/2

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20
Q

Diastereomers

A

Same molecular formula, same bond-to-bond connectivity, but not the same compound and are NOT mirror images of each other.

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21
Q

Dipole Moment

A

Occurs when center of positive charge does not coincide with center of negative charge. This makes the molecule POLAR.

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22
Q

Electrostatic Force

A

Nuclei pull on the electrons of the other atom to form the bond between atoms.

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23
Q

Enantiomers

A

Must have opposite absolute configurations at each and every chiral carbon. Has same physical and chemical properties.

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24
Q

Epimers

A

Diastereomers that differ at only one chiral carbon.

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25
Fischer Projection
Typical way to draw carbs. Vertical linnes oriented into the page. Horizontal lines oriented out of page.
26
Formal Charge
Number of electrons in the isolated atom - Number of electrons assigned to the atom = Formal Charge. EX. CN-. Charge on Carbon is -1. 4 (neutral carbon) - 5 (no. of electrons in CN-) = -1
27
Formula
Max number of optically active isomers = 2^n where n is the number of chiral centers.
28
Geometric Isomer
A type of diastereomers. Exist due to inability to rotate about a double bond. Making cis-isomers and trans-isomers. Different physical properties.
29
Hydrogen Bond
Strongest dipole-dipole interactions. When hydrogen is bonded to highly electronegative atom (N, O, F), creating large dipole moment and making the hydrogen positively charged. So when near another molecule, an intermolecular bond is formed between hydrogen and the N, O or F.
30
Index of Deficiency
AKA Degree of Unsaturation. Formal definition: Number of pairs of hydrogens a compound requires in order to become a saturated alkane.
31
Induced Dipoles
The polar molecule creates an electric field, pushing the electrons and nuclei in opposite directions, separating the centers of positive and negative charge.
32
Instantaneous Diple Moment
When the electrons in a bond move about the orbital, and at any given moment may not be distributed evenly creating a dipole moment.
33
Intermolecular Attractions
Attractions between separate molecules, occur solely due to dipole moments.
34
Isomers
Two molecules with same molecular formula but are different compounds.
35
Lewis Dot Structure
Using valence electrons to describe bonding within a molecule. There are 3 rules: 1) Find the total number of valence electrons for ALL atoms in the molecule. 2) Use 1 pair of electrons to form one bond between each atom. 3) Arrange the remaining electrons around the atoms, satisfying duet rule for Hydrogen and octet rule for other atoms.
36
London Dispersion Forces
Weakest dipole-dipole interactions. Occurs between two instantaneous dipoles.
37
Meso Compounds
Achiral. Two chiral centers in a single molecule may offset each other creating an optically inactive molecule. Plane of symmetry where two halves mirror each other.
38
Newman Projection
View straight down the axis of one of the sigma bonds. Intersecting lines and large circle are carbon atoms. Helps distinguish between conformers.
39
Observed Rotation
Direction and degree to which a compound rotates plane-polarized light.
40
Optically Active
Produces observed rotation, chiral compound.
41
Optically Inactive
Result in no observed rotation. Compounds have NO chiral centers or have internal mirror planes (meso compounds) that cancels each other out.
42
Plane-Polarized Light
The light that is shine on a molecule to observe its rotation.
43
Polarimeter
Uses to view a molecule's observed rotation.
44
Racemic Mixture
Mixing enantiomers in equal concentrations. Will NOT generate rotation of plane-polarized light since all chiral centers cancels each other out.
45
Relative Configuration
Two molecules have the same relative configuration about a carbon if they differ by only ONE substituent and the OTHER substituents are oriented identically about the carbon.
46
Resolution
Separation of enantiomers.
47
Resonance Structures
Representing delocalized electrons of pi bonds. Molecule must be conjugated unsaturated to have resonance.
48
sp
50% s character, 180, linear
49
sp2
33% s character, 120, trigonal planar
50
sp3
25% s character, 109.5, tetrahedral, pyramidal, bent
51
Specific Rotation
A standardized form of observed rotation. This is because the observed rotation is dependent upon polarimeter length, solution concentration, temp, type of wavelength used.
52
Stereoisomers
Same molecular formula, same bond-to-bond connectivity, but not the same compound (has chirality). Includes ENANTIOMERS and DIASTEREOMERS.
53
Steric Hindrance
When substituents crowd each other, such as in cis-isomers. Produces higher energy levels = higher heats of combustion.
54
Structural Isomer
Sam molecular formula, different bond-bond connectivity.
55
Trans-isomers
A geometric isomer with substituents on the opposite side. No dipole moment. Trans have WEAKER intermolecular forces leading to LOWER boiling points, due to HIGHER symmetry, trans molecules can form crystals readily, has HIGHER melting points. Written as E before molecular's name describing higher priority group is on the opposite side.
56
Valence
The number of bonds an atom usually forms. Memorize: Carbon (4), Nitrogen (3), Oxygen (2), Hydrogens/Halogens (1), Phosphorous (3), Sulfur (2)
57
Alkane
-C-C-
58
Alkene
-C=C-
59
Alkyne
-C(TRIPLE BOND)C-
60
Alcohol
#NAME?
61
Ether
R-O-R'
62
Amine
NHHR (primary), NHRR (secondary), NRRR (tertiary)
63
Aldehyde
R-CH=O
64
Ketone
R-CR'=O
65
Carboxylic Acid
R-COH=O
66
Ester
R-COR'=O
67
Amide
R-CNHH=O, R-CNRR=O
68
Alkyl
One hydrogen substituted from an alkane.
69
Halogen
image
70
Gem-dihalide
Halogens on same carbon.
71
Vic-dihalide
Halogens on different carbons.
72
Hydroxyl
#NAME?
73
Alkoxy
-OR
74
Hemiacetal
R-COHOR-H
75
Hemiketal
R-COHOR-R"
76
Carbonyl
C=O
77
Aryl
Phenyl as a substituent.
78
Functional Group Based on IUPAC Priority
Carboxylic acids - Aldehydes - Ketones - Alcohols - Amines - Alkynes - Alkenes - Alkanes
79
A conjugate base of an acid exhibits resonance, it is MORE or LESS stable. Is it a STRONGER or WEAKER acid?
resonance makes it more stable, so it has a stable conjugate base. A more stable conjugate base means a stronger acid. Example: Phenol is a stronger acid than ethanol.
80
Dextrotorary (+ or d)
Chiral compound that rotates light CLOCKWISE.
81
Levorotary (- or l)
Chiral compound that rotates light COUNTER-CLOCKWISE.
82
Ms-mesyl group
image
83
Ts-tosyl group
image
84
Acetyl
image
85
Acyl
image
86
image
87
Benzyl
image
88
Hydrazine
image
89
Hydrazone
image
90
Vinyl
image
91
Vinylic
image
92
Allyl
image
93
Nitrile
image
94
Epoxide
image
95
Enamine and Imine
image
96
Oxime
image
97
Nitro
image
98
Nitroso
image

MCAT Organic Chemistry (4 decks)

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