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Chemistry 351 > Terms 1 > Flashcards

Terms 1 Flashcards

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1
Q

Constitutional/structural isomers

A

same molecular formula but different structures

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2
Q

heteroatoms

A

atoms other than carbon and hydrogen, generally the reactive portion of organic molecules and the basis of functional groups

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3
Q

functional groups

A

the structural unit in a molecule that is responsible for its characteristic behaviour under a particular set of reaction conditions

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4
Q

stereoisomers

A

isomers with the same connectivity and molecular formulae but different arrangements of atoms in 3D space

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5
Q

conformational isomers

A

stereoisomers whose compounds can be interconverted by rotation about single bonds

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6
Q

configurational isomers

A

stereoisomers that cannot be interconverted by rotation about single bonds

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7
Q

geometric isomers

A

stereoisomers-configurational that does not have isomerism at a double bond, i.e. not mirror images

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8
Q

optical isomers

A

stereoisomers-configurational that are mirror images

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9
Q

diastereomers

A

optical isomers that are mirror images that are non-superimposable

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10
Q

enantiomers

A

optical isomers that has superimposable mirror images

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11
Q

electronegativity

A

a measure of the ability of an element to attract electrons toward itself

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12
Q

electrostatic potential maps

A

shows charge distribution within a molecule where red indicates higher electron density

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13
Q

resonance structures

A

differ only in the distribution of electrons in the Lewis structure, the connectivity of the individual atoms are the same in all resonance hybrids

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14
Q

resonance structures are necessary because:

A

electrons are often delocalized between two or more atoms, which is not depicted in Lewis diagrams

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15
Q

what are the rules for ranking resonance structure stability?

A
  1. all atoms neutral with FULL OCTET
  2. FULL OCTECT, negative formal charge=electronegative atom
  3. INCOMPLETE OCTET, negative formal charge=electronegative atom
  4. too many electrons in valence shell
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16
Q

electrophile

A

a reagent (or atom) that is attracted to areas of high electron density. An electrophilic species is electron poor and may have a formal positive charge associated with it

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17
Q

nucleophile

A

a reagent (or atom) that can donate electrons to an electrophilic centre. A nucleophile can be considered to be an electron rich species

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18
Q

what are two models that take into account the wave properties of electrons?

A

valence bond theory (connects structure and reactivity to hybridization) and molecular orbital theory (most powerful, but abstract)

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19
Q

each energy state corresponds to an:

A

orbital which can only contain two electrons

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20
Q

principal quantum number (n)

A

a whole number, integer, relates to the energy of the orbital

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21
Q

angular momentum quantum number (l)

A

designated by a letter (spdf, l=zero to n-1) and describes the shape of the orbital

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22
Q

magnetic quantum number (ml)

A

describes the spatial orientation of the orbital (+l to -l)

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23
Q

spin quantum number (ms)

A

describes the orientation of the two electrons in each orbital (either -1/2 or +1/2)

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24
Q

Pauli Exclusion Principle

A

no two electrons in the same atom can have the same set of four quantum numbers: MAX TWO ELECTRONS PER ORBITAL

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25
Aufbau Principle
orbitals are filled from the lowest-to-highest energy levels
26
Hund's Rule
if multiple orbitals of the same energy are available, the unoccupied orbitals will be filled first
27
node
area of zero possibility of finding electrons
28
bond length
inter-nuclear distance, determined based on energy minima
29
Bond dissociation energy
energy required to break bond
30
Molecular Orbital Model
electrons in a molecule occupy molecular orbitals (MOs) just as electrons in an atom occupy atomic orbitals (AOs)-expresses wave functions of molecular orbitals as sums and differences of wave functions of atomic orbitals
31
bond length is related to:
size of orbital (C-C bond is longer than C-H bond)
32
associate sigma (single) bonds with:
sp3 hybridization
33
associate pi (double) bonds with:
sp2 hybridization
34
associate triple bonds with:
sp hybridization
35
a double bond consists of:
a sigma bond and a pi bond
36
a triple bond consists of:
a sigma bond and two pi bonds
37
describe the molecular orbital model of chemical bonds:
electrons occupy molecular orbitals with max two electrons per MO. anti-bonds will cancel out with bonding orbitals, so no bonds formed
38
bond length is synonymous with:
inter-nuclear distance
39
the nitrogen atom in an amide bond is considered to be sp2 hybridized but:
the resonance structure allows it to be interconverted between sp2(pi bond) and sp3(all single bond) - but
40
generally, the more electrons shared around...
the more stable a molecule is, this is why extensive pi bond-electron overlap contributes to stability
41
the strength (and length/rotational ability) of a chemical bond can affect:
the properties of bond (and molecule)
42
in an exothermic reaction,
heat (energy) is released (delta H is negative)
43
in an endothermic reaction,
heat (energy) is absorbed (delta H is positive)
44
heat of combustion
the heat released when one mole of a compound undergoes complete combustion in oxygen (always exothermic, assume oxygen is in excess) - relates to stability
45
heat of formation
the heat released if one mole of a compound is formed from its component elements in their standard state (can be endo or exothermic)
46
Hess's law states:
that the ENTHALPY change for a reaction that converts starting materials to products is independent of the reaction pathway
47
characteristics of more stable products:
less exothermic heat of combustion (less heat released when completely combusted because more energy required to get it to combust & lower potential energy) and more exothermic heat of formation (more heat released when formed because only a little bit of energy required for actual formation)
48
all alkanes burn in air to give carbon dioxide and water, but heats of combustion increases with:
increasing number of carbons
49
heats of combustion decreases with:
chain branching because branched molecules are more stable (and thus have less potential energy)
50
bond dissociation should be HOMOLYTIC, meaning:
even/equal splitting of electrons in the bond, each atom gets an electron
51
isomers can differ in respect to:
stability (potential energy)
52
how can stability (potential energy) be measured?
by comparing heats of combustion
53
how to calculate change in heat of reaction?
(bonds made - bonds broken) = (heat of formation of products) - (heat of formation of reactants)
54
why are branched isomers more stable?
bond dissociation energy (energy required to break bonds) - larger bond dissociation energy relates to a stronger bond, harder to break, radicals will have higher potential energy and thus be less stable
55
what are 4 determinations for radical stability?
1. atom (larger atom forms a more stable radical) 2. resonance 3. induction (high electron density surrounding radical=more stable radical) 4. orbital (smaller orbitals=less stable radical)
56
reactions under thermodynamic control tend to result in:
the more stable product (if more than one product is possible)
57
reactions under kinetic control tend to result in:
the product that is formed at the fastest rate (if more than one product is possible)
58
what is the reaction mechanism for chlorination?
1. initiation (breaking of weakest bond to form halogen radicals) 2. propagation-SLOWEST RATE DETERMINING STEP (forms products and also more radicals) 3. termination (neutralize the radicals with each other)
59
regioselectivity
the preference for a reaction to form one regioisomer product over another (bonds to different TYPES of hydrogen)
60
the radical substitution of a hydogen by a halogen is regioselective because:
a hydrogen atom at certain positions are more preferentially replaced
61
what is the order of stability for alkyl radicals?
tertiary radical>secondary radical>primary radical (numbers relate to R groups bonded to C)
62
the more stable the free radical....
the weaker the original bond and the smaller the bond dissociation energy
63
activation energy is related to:
radical stability: lower Ea = more stable radical and more stable final product (usually)
64
relative stability of radical is generated with:
rate determining step (i.e. initiation and *propagation Ea)
65
chlorination of an alkane is only useful:
when all hydrogens in a molecule are equivalent (i.e. ring structures)
66
bromination is highly regioselective for:
substitution of tertiary hydrogens (H attached to C that is attached to three other C's)

Chemistry 351 (6 decks)

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