Structure and reactivity of organic molecules Flashcards
1
Q
heteroatoms
A
non metals on the periodic table which will be delta negative when bonded to carbon or hydrogen.
2
Q
heteroatoms symbol
A
A
3
Q
metals
A
atoms on the left side of the periodic table, including boron and silicon which will be delta positive when bonded to carbon or hydrogen.
4
Q
metal symbols
A
M
5
Q
order of electronegativity
A
M < H < C < A
6
Q
explanation of carbon hydrogen bond polarity
A
carbons electronegativity is 2.6 and hydrogens is 2.2 so the difference in electronegativity is not enough to make a polar covalent bond.
7
Q
delta negative atom in polar covalent bond
A
the atom which will have a greater pull on the bonding electrons and therefore is the nucleophile
8
Q
delta positive atom in polar covalent bond
A
the atom which has a weaker pull on the bonding electrons and therefore is the electrophile.
9
Q
what affects an atoms reactivity
A
dipoles from polar covalent bonds
10
Q
hydritic definition
A
where a hydrogen will have a greater pull on the bonding electrons
11
Q
protic definition
A
where a hydrogen will have a weaker pull on the bonding electrons.
12
Q
LUMO characteristics
A
the LUMO is an electrophile, meaning it will accept electron pairs from electron rich sites such as nucleophiles.
13
Q
HOMO characteristics
A
the HOMO is a nucleophile, meaning it will donate electron pairs to electron deficient sites such as an electrophile.
14
Q
electron pairs on organic atoms
A
carbon has 4 bonding pairs
nitrogen has 3 bonding and 1 non bonding
oxygen has 2 bonding and 2 non bonding
halogens will have 1 bonding and 3 non bonding electron pairs
15
Q
extra bond rule for organic atoms
A
an extra bond means a lone pair has formed a dative bond, resulting in a lone pair forming a bonding pair, giving the atom an extra positive charge.
16
Q
fewer bonds rule
A
if there are fewer bonds on an atom than normal it means that the atom has formed an extra lone pair, which will result in an extra negative charge.
17
Q
when can an atom form extra bonds
A
when the atom has a lone pair which it can use to form a dative covalent bond
18
Q
cationic species properties
A
their positive charge will mean the ion will accept electron pairs more easily, making it a stronger Lewis acid and electrophile.
19
Q
anionic species properties
A
their negative charge will mean that they will donate electron pairs more easily, meaning they will be a stronger Lewis base and nucleophile.
20
Q
Lewis acid
A
An electron pair acceptor, and therefore an electrophile
21
Q
Lewis base
A
An electron pair donator, and therefore a nucleophile
22
Q
Bronsted base definition
A
An electron rich proton acceptor.
23
Q
Bronsted acid definition
A
An electron deficient proton donator.
24
Q
important orbital type in Bronsted acids
A
Lumo
25
important orbital type in Bronsted bases
Homo
26
reason that carbon has stronger bonds than silicon
carbon's 2p orbitals will be smaller than silicon's 3p orbitals, which will result in a larger relative area of overlap in carbons molecular orbitals than silicon's molecular orbitals, resulting in shorter stronger bonds for carbon compounds allowing for carbon to form larger more complex molecules.
27
alcohol classifications
primary alcohols will have 1 carbon to carbon bond adjacent to the alcohol group.
secondary alcohols will have 2 carbon to carbon bonds adjacent to the alcohol group
tertiary alcohols will have 3 carbon carbon bonds adjacent to the alcohol.
28
amine classifications
primary means 1 N - C bond
secondary means 2 N - C bonds
tertiary means 3 N - C bonds.
quaternary means 4 N - C bonds
29
functional groups note
typically consisting of heteroatoms or carbon double/ triple bonds because they have pi electrons.
30
saturated molecule definition
where a molecule contains only sigma bonds
30
unsaturated definition
where a molecules contains a double or triple bond meaning it contains pi bonds.
31
unsaturated molecule types
Aryls
Alkene
Alkyne
31
alkyne functional group
c triple bond c
31
Aryl functional group
benzene ring attached to something
32
alkene functional group
c=c
32
alcohol functional group
OH
33
ether functional group
R - O - R
34
Amine functional group
N
35
Nitro compound functional group
N+=O
O-
36
aldehyde functional group
C = O
H
37
ketone functional group
C = O
R
38
carboxylic acid functional group
C = O
OH
39
ester functional group
C=O
O
C
40
acyl chloride functional group
C = O
Cl
41
Amide functional group
C =O
N
42
Acetal functional group
R - O - C - O - R
43
nitrile functional group
C triple bond N
44
acid anhydride functional group
C=O
O
C=O
45
oxidation classification
0 C - X
1 C - X
2 C - X
3 C - X
4 C - X
46
0 C - X
alkanes
47
1 C - X
molecules with 1 heteroatom bond + alkenes
48
2 C - X
molecules with 2 heteroatom bonds + alkynes
49
3 C - X
molecules with 3 heteroatom bonds
50
4 C - X
molecules with 4 heteroatom bonds
51
rules for oxidation classifications
look only at the atom with the highest number of C - X bonds to determine oxidation classification.
52
reduction definition
reduction is a gain of electrons.
this can be done by the loss of an electronegative atom, which would pull electron densitity away from the whole molecule.
or this can be done by gaining an electropositive atom which will donate electron density to the whole molecule.
hydrogen is an electropositive atom, oxygen is an electronegative atom.
53
oxidation definition
where there is a loss of electrons
this could be through the addition of an electronegative atom, which will pull electron density away from the molecule.
or this could be through the removal of an electropositve atom, which will donate electron density to the molecule.
54
reason for alkenes being part of alcohol oxidation classification
one of the carbons in the unsaturated double bond will gain hydrogen, meaning it is reduced, whereas the other carbon in the unsaturated carbon to carbon double bond will gain a heteroatom, meaning it will be oxidized.
this will result in redox neutral reaction/ transformation.
55
reason that alkynes are part of the aldehydes classification
One of the carbons in the unsaturated carbon to carbon triple bond will gain 2 hydrogens meaning it will be reduced twice, whereas the other carbon will gain a double bond with an oxygen meaning it is oxidized twice.
this will result in a redox neutral transformation between any 2 C - X molecule and an alkyne.
56
priority naming rule
if there is multiple functional groups the group with the highest oxidation classification will go first, if they have the same priority then the group which comes first in the alphabet goes first.
57
rule for choosing which side to go from when naming a molecule
name from the side which will give the highest priority group the lowest number.
58
ortho
means 1,2 on cyclic structures
59
para
means 1, 4 on cyclic structures
60
meta
means 1, 3 on cyclic structures
61
explanation for priority of electron donation in nucleophilic substitution
electron pairs will be donated from the HOMO meaning that the highest energy orbitals will be donated first meaning non bonding electrons first, then pi bonding orbitals, then sigma bonding orbitals.
62
order of priority of electron donation
n - non bonding electron pair in hybridized P orbital
π - pi bonding orbital
σ - pi bonding orbital
63
order of priority of electron receiving
P - unhybridized unoccupied P orbital
π* - antibonding pi orbital
σ* - antibonding sigma orbital
64
Bond order formula
(bonding electrons - antibonding electrons) /2
65
halogen bonding properties rule
as you go down the halogen group the greater the size of the valence P orbitals, which will result in a smaller relative overlap of when forming bonding molecular orbitals with another atom such as carbon, meaning as you go down the group the bond length will increase and the bond strength will decrease, which will result in halogens further down the group being more reactive.
66
sp3 hybridisation rules
if the molecule only has single bonds it will be sp3
If you don't know use VSEPR to check for tetrahedral structure.
67
sp2 hybridisation rules
if the molecule has a double bond it will be sp2
If you don't know check VSEPR for trigonal planar electron arrangement.
68
sp hybridisation rule
if the molecule has a triple bond it will be sp hybridised
if you dont know check VSEPR and look to see whether it is linear.
69
atoms which don't hybridize
hydrogen because it only has 1 electron
70
molecular orbital diagram process
draw out normal electronic configuration
draw out the hybridized electronic configuration
overlap valence hybrid orbitals and form appropriate bonding and antibonding molecular orbitals
71
hybrid orbital energy explanation
sp3 orbitals will have higher energy than sp2 due to there being a greater ratio of P to S orbitals in sp3, meaning there is greater p character and the P orbitals will pull the degenerate hybrid orbitals further from the nucleus.
72
nucleophilic substitution process
the electron pair from the non bonding occupied p orbital will attack the delta positive atom in the C - X bond which will allow the bonding electrons to shift onto the delta negative atom, breaking apart the C - X bond.
72
Homolytic fission process
An electron in the bonding orbital will absorb energy from the electromagnetic spectrum ( typically UV light) which will promote the electron from the HOMO to the LUMO, meaning the electron will now sit in the lowest antibonding orbital, causing the bond to cleave.
73
Isoelectric species definition
two species with the same number of electrons, which therefore have very similar electronic structures and chemical properties
74
isoelectric carbocation
boron atom since a carbon atom with one less electron will have the same structure as boron.
75
isoelectric carbanions
nitrogen because a carbon atom with an extra electron will have the same structure as nitrogen.
76
conjugated system definition
A series of alternating single and double bonds which will allow for delocalized π electrons across many atoms bonding molecular orbitals.
77
conjugated system properties
lower energy molecular orbitals
lower HOMO to LUMO gap will mean a greater reactivity since electrons can more easily be promoted to the antibonding orbital.
colour can occur due to visible wavelengths of light being absorbed to promote electrons from the homo to the lumo.
78
important features of conjugated systems
conjugated systems will allow for delocalized electrons, which will mean that resonance structures are possible.
79
resonance structure definition
when delocalized electrons will travel between different atoms bonding orbitals meaning that the molecules eletronic structure is in between the two different structures
80
types of resonance structures
π - π*
n - π
p - π/ p - n
σ - p
81
π - π* resonance
normal
π electrons from a double bond will travel to the π orbital of a single bond, forming a double bond.
π electrons from a double bond two bonds over from the original bond will travel to the π orbital of the single bond forming a double bond.
if no second single bond is available then the π electrons will form a non bonding electron pair on the atom, causing a positive and negative charge on the molecule.
82
n - π resonance
electrons from the non bonding occupied p orbital will travel onto the unoccupied π orbital of the single bond.
π electrons from the double bond will travel onto the single bonds unoccupied π orbital forming a double bond.
if there is no available second single bond then the electrons will form a non bonding electron pair on the next atom.
83
P - π/ P - n resonance name
mesomeric effect
84
mesomeric effect resonance structure
electrons will move from the double bonds π orbital or the non bonding electron pairs occupied P orbital and occupy an unoccupied P orbital , causing one atom to gain a positive charge and another atom to lose a positive charge.
85
σ - π conjugation names
positive inductive effect hyperconjugation
86
σ - π resonance features
only occurs in secondary and tertiary carbocations
87
σ - π resonance process
the R groups on the secondary or tertiary carbocation will have hydrogen σ bonds which will be parallel to the unoccupied P orbital, which will allow for the σ orbitals to give away their electrons partially, stabilizing the positive charge of the carbocation.
88
Ka definition
the measure of how easily an acid will donate a proton to another species.
89
pKa formula
pKa = -log Ka
90
pKa relationship with Ka
as Ka increases the pKa decreases.
91
acid base organic reaction
the non bonding electron pair on the base will go onto the delta positive hydrogen of the acid, meaning the electrons of the acid - hydrogen bond will go onto the acid, which will mean that the hydrogen will be donated to the base.
92
conjugate base
the base of the reverse reaction, which is formed by the acid donating its proton
93
conjugate acid
the acid of the reverse reaction - which is formed by the base accepting a proton.
94
rule for strength of acids and bases
if the acid is a strong acid then the conjugate base must be a weaker base
if the base is a strong base then the conjugate acid must be a weaker acid.
vice versa
95
strength of acid in relation to Ka and pKa explanation
ka is the measure of how easily an acid will donate its proton, which is to say how strong the acid is, so a high Ka means a strong acid, pKa is the negative log of Ka so a low pKa will mean a strong acid
96
what is the effect of an anion being localized
localized anions electrons remain in fixed orbitals, meaning the anion will be more willing to give up its non bonding electron pairs, this will mean that the conjugate base will be stronger, meaning the acid will be weaker and therefore the acid will have a higher pKa
97
delocalized anions effect on acid strength
a delocalized anion will have electrons which move freely between different bonding orbitals, which will mean these electron pairs will be donated less easily, resulting in a weaker conjugate base, which will result in a stronger acid and therefore a lower pKa
98
structural / constitutional isomers
molecules with the same molecular formula, but a different connectivity of atoms and therefore different chemical properties
99
possibilities for constitutional isomers
they have functional groups rearranged into different locations
they have different functional groups present
100
stereoisomers definition
molecules with the same molecular structure and connectivity, but a different 3D arrangement in space.
101
Enantiomers
two stereoisomers which are non superimposable mirror images of each other, with a stereogenic center
102
different names for a stereogenic center
chiral center
stereo center
103
stereogenic center definition
a carbon atom with 4 distinct groups attached to it.
104
chirality requirements
a molecule is chiral if it contains a stereogenic center and has no planes of symmetry.
105
rule for chirality of different stereoisomers
'normal' enantiomers must always be chiral
diasterioisomers can be chiral or non chiral
geometric isomers can never be chiral
106
up position for stereoisomers
wedge coming out of the page
107
down position for stereoisomers
hashed line going into the page
108
configurations of stereoisomers definition
configurations are two different stereoisomers where bonds need to be broken and reformed to change between the two molecules.
109
how to distinguish a configuration of enantiomers
two different groups will be opposite each other in both enantiomers
if unsure make both molecules.
110
conformations in stereoisomers definition
where there are two different structures of the same molecule with different energies and these different structures can be changed between by rotating bonds.
111
R and S isomer distinguishing process
draw molecule and label the groups around the chiral center 1-4, 1 being the group with the highest atomic number, 4 being the group with the lowest atomic number.
flip the molecule around so the 4 group is in the down position.
rotate the steering wheel so that 1 is in the up position
if groups go 1-2-3 clockwise it is an R
if groups go 1-2-3 anticlockwise it is S
112
R enantiomers
clockwise
113
S enantiomer
anticlockwise
114
enantiomers properties
enantiomers will have the same physicochemical and spectroscopic properties in normal environments
115
racemic mixtures definition
where there is a mixture of two enantiomers of equal proportions.
116
α D = 0 meaning
the molecule doesn't rotate polarized light
117
α D = 0 examples
racemic mixtures
geometric isomers
Anti - diasterioisomers when there is a plane of symmetry.
118
why does α D = 0 in Anti - diasterioisomers when there is a plane of symmetry.
when there is a plane of symmetry in Anti - diasterioisomers it means the RS and SR configurations are identical, meaning they wont rotate polarized light.
119
α D in R and S rule
there is no relationship between R and S and +ve or-ve values, but if R is +30 then S is -30
120
number of enantiomers formula
2^x
where x is the number of stereogenic centers.
121
diasterioisomers definition
stereoisomers with 2 stereogenic centers which are not mirror images but have distinct relative configurations.
122
diasterioisomers chirality
if the molecule has no plane of symmetry it will be chiral from two different stereogenic centers
if the molecule has a plane of symmetry it will be achiral.
123
syn
RR configuration or SS configuration
124
anti
RS configuration or SR configuration
125
anti - diasterioisomers when there is a plane of symmetry
the RS and SR enantiomers will be identical molecules
126
geometric isomers
molecules containing a bond with restricted rotation.
127
E
geometric isomers with highest priority groups on opposite sides
128
Z
geometric isomers with highest priority groups on the same side
129
cis
same side highest priority in cyclic structures
130
trans
opposite side highest priority in cyclic structures
131
difference in energy for conformations rule
the greater the energy required for a bond top be rotated, the greater the difference in energy between two different conformations.
132
energy required to rotate different types of bond
single bonds have low energy for rotation.
π - π conjugations will have a medium energy for rotation due to the delocalized π electrons giving the bond double bond character
n - π conjugations will have high energy for rotation due to the delocalized electrons giving the single bond a high double bond character.
double bonds have impossible rotational energy.
133
Newman diagram
face on looking down the bond axis
134
sawhorse/ perspective diagram
side on looking at the bond axis in the x axis of the page.
135
staggered antiperiplanar structure
x groups are 180 degrees away from each other, lowest energy conformation due to 6 σ 6σ* hyperconjugations.
136
staggered gauche conformation
x groups 60 degrees away from each other, medium energy conformation due to 6 σ 6σ* hyperconjugations.
137
elliptical syn periplanar structure
0 degrees between x groups, highest energy conformation due to 3σ 3σ destabilizations.
138
cyclohexane configurations
chair and boat
chair is the low energy configuration
boat is the high energy configuration
139
chair conformation structure of hydrogens
one hydrogen will be axial up and one hydrogen will be equatorial down
or one hydrogen will be axial down and one hydrogen will be axial up
140
axial hydrogens
hydrogens which are vertical
141
equatorial hydrogens
hydrogens which are almost horizontal
142
changing between different conformation
change an axial group to an equatorial group
143
changing between different configurations
change an up position to a down position
