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MCAT OChem > Molecular Structure > Flashcards

Molecular Structure Flashcards

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MCAT 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
Q

character

A

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

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26
Q

sp bond angles and shape

A

180

linear

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27
Q

sp2 bond angles and shape

A

120

trigonal planar

28
Q

sp3 bond angles and shape

A

109.5

tetrahedral, pyramidal, or bent

29
Q

sp3d bond angles and shape

A

90, 120

trigonal-bipyramidal, seesaw, t-shaped, or linear

30
Q

sp3d2 bond angles and shape

A

90, 90

octahedral, square pyramidal, or square planar

31
Q

delocalized electrons result from ….

A

shifting of pi bonds

32
Q

resonance structures

A

represent molecules with delocalized electrons

33
Q

4 rules for writing resonance structures

A

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
Q

2 conditions for resonance to occur

A

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
Q

dipole moment occurs when…

A

the center of positive charge on a molecule or bond does not coincide with the center of negative charge

36
Q

induced dipoles

A

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
Q

instantaneous dipole moment

A

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
Q

intermolecular attractions occur…

A

due to dipole moments

39
Q

hydrogen bond

A

H - F, O, or N
strongest dipole-dipole interaction
responsible for high boiling point of water

40
Q

London Dispersion Forces

A

weakest dipole-dipole force, between 2 instantaneous dipoles

responsible for phase changes of nonpolar molecules

41
Q

isomers

A

unique molecules with the same molecular formula, same molecular formula but different compounds

42
Q

conformational isomers / conformers

A

different spatial orientations of the same molecule, not true isomers

43
Q

chiral molecules

A

differ from their reflections, have “handedness”

44
Q

any carbon is chiral when….

A

it is bonded to four different substituents

45
Q

absolute configuration

A

only way to physically describe the orientation of atoms about a chiral center
R (clockwise circle) or S (counterclockwise circle)

46
Q

relative configuration

A

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
Q

observed roation

A

direction and degree to which a compound rotates plane-polarized light

48
Q

polarimeter

A

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
Q

plane polarized light

A

consists of photons with their electric fields oriented in the same direction

50
Q

optically inactive

A

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
Q

optically active

A

when plan-polarized light is projected through such a chiral compound, the orientation of its electric field is rotated
+/d = clockwise
-/l = couterclockwise

52
Q

specific rotation

A

standardized from

53
Q

stereoisomers

A

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
Q

enantiomers

A

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
Q

racemic mixture

A

when enantiomers are mixed together in equal concentrations

do not rotate plane polarized light

56
Q

resolution

A

separation of enantiomers

57
Q

diastereomers

A

not mirror images, not same compound
same molecular formula and same bond to bond connectivity
ex: geometric isomer

58
Q

geometric isomer

A

due to hindered rotation around double bold
cis vs. trans
*have different physical properties

59
Q

___ molecules have dipole moment while ___ molecules do not

A

cis molecules have dipole moment, trans do not

60
Q

melting and boiling points of geometric isomers

A

cis have higher boiling points: dipole moments –> stronger intermolecular forces
cis have lower melting points: lower symmetry –> do not form crystals as readily

61
Q

E vs Z

A 
E = highest priority (greatest weight) on opposite sides
Z = on zame side
62
Q

max number of optically active isomers =

A

2^n (n= number of chiral centers)

63
Q

meso compounds

A

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
Q

epimers

A

diastereomers that differ at only one chiral carbon

65
Q

anomers

A

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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