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MCAT OChem > Molecular Structure > Flashcards

Molecular Structure Flashcards

1
Q 
valence of:
carbon
hydrogen
nitrogen
oxygen
phosphorous
sulfur 
halogens
A 
carbon =4
hydrogen =1
nitrogen =3
oxygen = 2
phosphorus = 3
sulfur =2 
halogens are monovalent but capable of making more than 1 bond, other than fluorine)
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2
Q

formal charge

A

of e-s in isolated atom, minus the # of e-s assigned to the atom in the Lewis structure

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3
Q

dash formula

A

shows bonds between atoms but not 3D structure

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4
Q

condensed formula

A

does not show bonds, CH3NH2

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5
Q

bond-line formula

A

line intersections, corners, and ending represent C

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6
Q

Fischer projection

A

vertical lines are assumed to be oriented into the page, horizontal lines out of page

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7
Q

Newman projection

A

view straight down axis of one of the sigma bonds

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8
Q

index of deficiency

A

number of pairs of hydrogens a compound requires in order to become a saturated alkane (2n+2 hydrogens)
count halogens as hydrogens
ignore oxygen atoms
count nitrogen atoms as one half a hydrogen atom

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9
Q

1 degree of unsaturation

A

a double bond or cyclic structure

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10
Q

triple bond is ___ degrees of unsaturation

A

2

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11
Q

ether

A

R-O-R’

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12
Q

amine

A

R-N-H (-H) or with R’ and R’’

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13
Q

aldehyde

A

R-C=O(-H)

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14
Q

ketone

A

R-C=O(-R’)

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15
Q

carboxylic acid

A

R-C=O(-OH)

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16
Q

ester

A

R-C=O(-O-R’)

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17
Q

amide

A

R-C=O(-NH2)

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18
Q

prefix for 1-10 for alkanes

A

meth, eth, prop, but, pent, hex, hept, oct, non, dec

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19
Q

coordinate covalent bond

A

one nucleus can donate both electrons

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20
Q

electrons are at their lowest energy level when ……

A

when they form a bond because they have minimized their distance from both nuclei

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21
Q

sigma bond

A

bonding pair of electrons are localized directly between the two bonding atoms
most stable form of covalent bond
first type of covalent bond formed between any 2 atoms

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22
Q

pi bond

A

if additional bonds from between 2 sigma bonded atoms

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23
Q

each additional bond between atoms ____ the distance between the bonded atoms

A

shortens –> greater bond strength

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24
Q

___ bond are more reactive

A

pi bonds, electrons further from nucleus than in sigma bond, at higher energy level/less stable

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25
character
hybrid orbital resembles in shape and energy the s and p orbitals from which it is formed to the same extent that s and p orbitals or used to from it. sp2 = 33.3% s character and 66.7% p character
26
sp bond angles and shape
180 | linear
27
sp2 bond angles and shape
120 | trigonal planar
28
sp3 bond angles and shape
109.5 | tetrahedral, pyramidal, or bent
29
sp3d bond angles and shape
90, 120 | trigonal-bipyramidal, seesaw, t-shaped, or linear
30
sp3d2 bond angles and shape
90, 90 | octahedral, square pyramidal, or square planar
31
delocalized electrons result from ....
shifting of pi bonds
32
resonance structures
represent molecules with delocalized electrons
33
4 rules for writing resonance structures
atoms must not be moved (only e-s) number of unpaired e-s remains constant resonance atoms must lie in same plane proper Lewis structures used
34
2 conditions for resonance to occur
species must contain an atom either with a p orbital or an unshared pair of electrons atoms must be single bonded to an atom that possesses a double or triple bond
35
dipole moment occurs when...
the center of positive charge on a molecule or bond does not coincide with the center of negative charge
36
induced dipoles
dipole moment momentarily induced in an otherwise nonpolar molecule or bond by a polar molecule, ion, or electric field common in nature, weaker than permanent dipoles
37
instantaneous dipole moment
because the electrons in a bond move bout the orbital and at any given moment may not be distributed exactly between the two bonding atoms even when teh atoms are identical can induce dipole in neighboring atom
38
intermolecular attractions occur...
due to dipole moments
39
hydrogen bond
H - F, O, or N strongest dipole-dipole interaction responsible for high boiling point of water
40
London Dispersion Forces
weakest dipole-dipole force, between 2 instantaneous dipoles | responsible for phase changes of nonpolar molecules
41
isomers
unique molecules with the same molecular formula, same molecular formula but different compounds
42
conformational isomers / conformers
different spatial orientations of the same molecule, not true isomers
43
chiral molecules
differ from their reflections, have "handedness"
44
any carbon is chiral when....
it is bonded to four different substituents
45
absolute configuration
only way to physically describe the orientation of atoms about a chiral center R (clockwise circle) or S (counterclockwise circle)
46
relative configuration
two molecules have the same relative configuration about a C is they differ by only one substituent and the other substituents are oriented identically about the C not related to absolute configuration inverted in SN2 reactions
47
observed roation
direction and degree to which a compound rotates plane-polarized light
48
polarimeter
screen out photons with all but one orientation of electric field resulting light consists of photons with their electric fields oriented in the same direction: plane polarized light
49
plane polarized light
consists of photons with their electric fields oriented in the same direction
50
optically inactive
no single molecular orientation is favored so the net result is no rotation of the plan of the electric field may be compounds with no chiral centers or molecules with internal mirror planes (meso compounds)
51
optically active
when plan-polarized light is projected through such a chiral compound, the orientation of its electric field is rotated +/d = clockwise -/l = couterclockwise
52
specific rotation
standardized from
53
stereoisomers
two molecules with the same molecular formula and the same bond-to-bond connectivity that are not the same compound must contain at least 1 chiral center
54
enantiomers
nonsuperimposable mirror images, opposite absolute configurations at each chiral carbon rotate plane polarized light in opposite directions at an equal degree have same physical and chemical properties except for interactions with other chiral compounds and polarized light
55
racemic mixture
when enantiomers are mixed together in equal concentrations | do not rotate plane polarized light
56
resolution
separation of enantiomers
57
diastereomers
not mirror images, not same compound same molecular formula and same bond to bond connectivity ex: geometric isomer
58
geometric isomer
due to hindered rotation around double bold cis vs. trans *have different physical properties
59
___ molecules have dipole moment while ___ molecules do not
cis molecules have dipole moment, trans do not
60
melting and boiling points of geometric isomers
cis have higher boiling points: dipole moments --> stronger intermolecular forces cis have lower melting points: lower symmetry --> do not form crystals as readily
61
E vs Z
``` E = highest priority (greatest weight) on opposite sides Z = on zame side ```
62
max number of optically active isomers =
2^n (n= number of chiral centers)
63
meso compounds
two chiral centers in single molecule offset each other creating an optically inactive molecule have plane of symmetry through center that divides them into two halves that are mirror images of each other *achiral and optically inactive
64
epimers
diastereomers that differ at only one chiral carbon
65
anomers
two possible diasteriomers that can form if a ring closure occurs at the epimeric carbon anomeric carbon = chircal carbon of anomer

MCAT OChem (4 decks)

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