Organic chemistry Flashcards
(244 cards)
1
Q
What is a covalent bond?
A
- shared valence e⁻ pair bw 2 nuclei
- ∴ E(mol) < ΣE(atoms)
- directional bond (specific orientation bw atoms)
2
Q
How are covalent bonds formed between atoms?
A
overlap of atomic orbitals → ↑e⁻ density bw nuclei
attraction: nuclei ↔ shared e⁻ pair > nucleus–nucleus repulsion
bond forms at optimal internuclear distance (min potential E)
3
Q
How does the energy of a molecule compare to the sum of the energies of separate atoms in a covalent bond?
A
E(mol) < ΣE(atoms)
4
Q
What are the primary types of bonding in chemistry?
A
primary bonding:
- covalent
- ionic
- metallic
5
Q
What are secondary bonds and how do they differ from primary bonds?
A
secondary bonding:
- dispersion (london) forces
- d-d interactions
- H bonding
weaker than primary
6
Q
What are dispersion forces and dipole-dipole (D-D) interactions?
A
dispersion → temp dipoles in non-polar mols
D-D → perm dipoles attract e.g. HCl
7
Q
What are the key characteristics of covalent bonding?
A
- 2 valence e- per bond
- form stable mols
- common in non-metals
- directionality → defines mol shape
- obeys octet rule (except H: duet)
- multiple bonds possible (double/triple)
- e⁻ density concentrated bw nuclei
8
Q
What does the octet rule state regarding the stability of compounds?
A
compounds most stable when have full valence shell = 8 e-
9
Q
Why do noble gases have a stable configuration, and how does this relate to the octet rule?
A
Grp 18 → have full valence shell already (8 e-) = octet rule
10
Q
How do you determine the number of valence electrons in an element?
A
corresponds w grp number
transition metals = exception
11
Q
How do you calculate the total number of valence electrons in a molecule?
A
add together valence e- in constituent atoms
12
Q
What is the importance of valence electrons in covalent bonding?
A
covalent bond = formed bw 2 valence e- → 2 atoms ‘share’ so they can achieve octet = more stable conformation
13
Q
What is a Lewis structure, and how is it used to represent molecules?
A
draws valence e- and covalent bond
14
Q
What should you do with leftover electrons after completing the octet rule for all atoms?
A
leftover e- → lone pairs on central atom esp. if period 3+ (can have expanded octet)
extra e- → consider formal charges
15
Q
Where do you place the remaining electrons if the molecule contains atoms in period 3 or above?
A
on central atom
16
Q
What are formal charges in Lewis structures, and why are they important?
A
hypthetical charges assigned to atoms
assumes e- in chem bonds = shared equally
helps det most stable/likely lewis structure (FC closer to 0)
neg FC goes on more electroneg atom
17
Q
What is the octet rule, and why is it important in chemical bonding?
A
based on noble gas config = most stable
18
Q
What are some examples of molecules where the octet rule is obeyed?
A
CNOF + most main grp elems
19
Q
What are the exceptions to the octet rule?
A
H → only 2 e⁻ (duet rule)
B, Be → often less than 8
3rd period+ → can expand octet (e.g. P, S, Cl)
20
Q
How do elements in period 3 and beyond expand their valence shells beyond the octet?
A
use d-orbitals (available from 3rd period on) to hold extra e-
Enables bonding with more atoms → ↑ stability for larger central atoms
21
Q
Provide an example of a molecule that follows the expanded octet rule.
A
PCl5 (10e- on P)
22
Q
Why can phosphorus (P) expand its valence shell beyond the octet rule?
A
3rd period → has access to 3d orbitants → hold extra e-
23
Q
What are multiple bonds, and how are they formed in covalent bonding?
A
2+ shared e- pairs bw atoms
involve σ (sigma) + π (pi) bonds:
1st bond = σ
2nd & 3rd = π (side-on overlap of p orbitals)
24
Q
How do multiple bonds help atoms obey the octet rule?
A
gives period 1 & 2 elems access to more e-
25
Provide an example of a molecule that forms a double bond.
CO2, O2
26
Provide an example of a molecule that forms a triple bond.
N2
27
What is resonance in the context of Lewis structures?
when 2+ valid lewis structures can be drawn for same mol
28
Why is it necessary to use two different Lewis structures for the same molecule in resonance?
Neither individual structure fully represents the true bonding of the molecule. Both are needed to describe it correctly.
29
How does the actual structure of a molecule with resonance compare to the individual Lewis structures?
actual struc = hybrid of all resonance forms → more stable
bonds in resonance = intermed length/strength bw single/double bonds
30
What is a resonance arrow, and what does it indicate?
Shown by ↔ between structures
31
How do formal charges help in determining the correct resonance structure?
most stable resonance struc has fewest FCs
32
How do you calculate bond order in a molecule with resonance?
Bond Order= Total number of bonds in all resonance structures /
Number of resonance structures
e.g. BO of NO3- =2 → actual bond length/strength = somewhere bw single + double bond
33
What does the electron delocalization model describe?
how e- in certain mols X confined to single bond/atom - instead stread out over multi atoms/bonds → max stability
34
How are bonding electrons distributed in molecules with resonance, such as ozone (O₃)?
bonding e- spread across multi atoms/bonds i.e. delocalised
O3: consists of 1 single + 1 double bond - location of double bond alternates bw 2 O atoms
35
How do you calculate bond order in a molecule with delocalized electrons?
Bond order= Total number of bonds /
Number of bonding sites
36
What is a sub-octet Lewis structure?
<8 valence e-
37
Provide an example of a molecule that has fewer than 8 valence electrons around the central atom.
H - duet
Be - often forms bonds w only 4 valence e-
B - often forms bonds w only 6 valence e-
38
Why does boron (B) in BF₃ have fewer than 8 valence electrons?
B can form stable mol w only 6 valence e- bc size its size + high electronegativity of F atoms
39
What is a Lewis acid, and how does it relate to molecules with sub-octets?
e- PAIR acceptor
→ covalent bond formation
40
What is a radical, and how is it different from other species?
chem spp that contains 1+ unpaired e- in valence shell
highly reactive
41
Why are radicals often highly reactive?
bc unpaired e- → unstable
42
What is the relationship between the number of electrons and the formation of radicals?
e- removed from/added to stable mol → unpaired e- → radical formation
ODD # E-
43
How can you identify if a molecule has formal charges and where they are located?
FC = VE - (LP + 1/2*BE)
VE: valence e-
LP: lone pair e- on atom
BE: bonding e- (shared in covalent bonds - each bond = 2e- shared)
44
What are the steps to determine molecular geometry using VSEPR theory?
🧪 1. Draw Lewis structure
📍 2. Count e⁻ domains (regions of e⁻ density) around central atom
📊 3. Determine e⁻ domain geometry (EDG)
🔍 4. Determine molecular shape (actual geometry) based on lone pairs
45
How do you count e- domains?
Bond = 1 domain (single, double, triple = still 1)
Lone pair = 1 domain
46
How do regions of electron density determine molecular shape?
2 domains → linear
3 domains → trigonal planar
4 domains → tetrahedral
5 domains → trigonal bipyramidal
6 domains → octahedral
47
What is the difference between electron pair geometry (EPG) and molecular geometry?
lone pairs affect molecular shape differently than bonds:
3 domains:
3 bonds → trigonal planar
2 bonds + 1 LP → bent
4 domains:
4 bonds → tetrahedral
3 bonds + 1 LP → trigonal pyramidal
2 bonds + 2 LP → bent
5 domains:
4 bonds + 1 LP → see-saw
3 bonds + 2 LP → T-shaped
2 bonds + 3 LP → linear
6 domains:
5 bonds + 1 LP → square pyramidal
4 bonds + 2 LP → square planar
48
What is the bond angle in a linear geometry?
180*
49
What is the bond angle in a trigonal planar geometry?
~120*
50
What is the bond angle in a tetrahedral geometry?
~109.5*
51
What are the bond angles in a trigonal bipyramidal geometry?
90° → between axial ↔ equatorial positions
120° → between equatorial ↔ equatorial positions
180° → between the two axial positions
52
What is the bond angle in an octahedral geometry?
180* and 90*
53
What shape does a molecule with 4 bonding pairs and 1 lone pair have?
see-saw
54
What shape does a molecule with 3 bonding pairs and 1 lone pair have?
trigonal pyramidal
55
What shape does a molecule with 2 bonding pairs and 2 lone pairs have?
bent
56
How does the presence of lone pairs affect molecular geometry?
↑ lone pairs → ↑ repulsion → ↓ bond angles → ideal geometry distorted
57
How do you draw the 3D geometry of a molecule based on its VSEPR shape?
Solid line (—): bond in plane of paper
Wedge (▲): bond coming out toward you
Dash (▭ or dashed line): bond going back away from you
58
What happens when two atomic orbitals overlap?
↑ electron density between nuclei → covalent bond → Electrons are localized between bonded atoms
59
Describe the two types of overlaps/covalent bonds.
σ (sigma) bond = end-to-end overlap (strong, 1st bond in any pair)
π (pi) bond = side-to-side overlap (weaker, forms 2nd/3rd bonds in multiple bonds)
60
What determines bond length according to the valence bond model?
extent of orbital overlap (influ by atomic radii, BO, hybridisation, electroneg)
↑ overlap → ↑ bond strength → ↓ bond length
61
What is hybridisation?
mixing of orbitals → form hybrid orbitals → specific shapes/energies for covalent bonding
62
How does a carbon atom hybridise in methane (CH₄)?
- C undergoes sp hybridisation in CH4
- 1x 2s orbital + 3x 2p orbitals mix → 4x equivalent sp3 hybrid orbitals
- sp3 orbitals arranged in tetrahedral geo (109.5* bond angles)
- sp3 overlaps w 1s orbital in H → 4x sigma (σ) bonds
63
What is the geometry of an sp³-hybridised oxygen atom, such as in H₂O?
bent (v-shaped)
64
What is the geometry of an sp³-hybridised nitrogen atom, such as in NH₃?
trigonal pyamidal
65
How can you determine the hybridisation of an atom based on its bonding and lone pairs?
1. Count the regions of electron density (bonds and lone pairs) around the atom:
2. Match the number of regions of electron density to hybridization:
2 regions → sp hybridization (linear geometry).
3 regions → sp² hybridization (trigonal planar geometry).
4 regions → sp³ hybridization (tetrahedral geometry).
5 regions → sp³d hybridization (trigonal bipyramidal geometry).
6 regions → sp³d² hybridization (octahedral geometry).
66
What is a molecular orbital?
67
How are molecular orbitals formed from atomic orbitals?
68
What is the difference between bonding and antibonding molecular orbitals?
69
What is the bond angle in CH₄ (methane)?
70
What is the C–H bond strength in CH₄?
71
What are the van der Waals radii of carbon and hydrogen?
72
What are the melting and boiling points of methane?
73
What is the C–C bond length and strength in ethane (C₂H₆)?
74
What is the H–C–C bond angle in ethane?
75
What are the melting and boiling points of ethane?
76
What is the general formula for a saturated hydrocarbon (alkane)?
77
What is structural isomerism?
78
How do you draw the tetrahedral form of an alkane?
79
How do you draw the skeletal structure of an alkane?
80
What are the IUPAC rules for naming alkanes?
81
How do you identify the longest carbon chain in an alkane?
82
How do you number the chain to find the lowest set of locants?
83
How do you name substituents in an alkane?
84
How do you apply alphabetical order in naming alkyl groups?
85
How do you draw the structure of an alkane given its IUPAC name?
86
What is the chemical formula of methane, ethane, propane, and butane?
87
What are some common uses of methane, propane, and butane?
88
What carbon chain lengths are found in petrol, diesel, and heating oil?
89
What is conformational isomerism?
90
What causes conformational isomers to exist?
91
How do conformational isomers differ from other types of isomers?
92
Who were awarded the Nobel Prize in 1969 for the concept of conformation?
93
What is a Newman projection?
94
How do you draw a Newman projection?
95
How can you identify different conformers from a Newman projection?
96
What do the front and back circles represent in a Newman projection?
97
How is torsional strain visualised in a Newman projection?
98
What is a dihedral angle?
99
How is a dihedral angle measured?
100
What is the dihedral angle between substituents in a staggered conformation?
101
What is the dihedral angle between substituents in an eclipsed conformation?
102
How do dihedral angles help visualise conformers?
103
What are the two main conformers of ethane?
104
Which ethane conformer is most stable, and why?
105
What type of strain is present in the eclipsed conformer of ethane?
106
What is the energy barrier to rotation in ethane?
107
How does the energy diagram of ethane explain the difference between staggered and eclipsed conformers?
108
What are the names of the staggered conformers of butane?
109
What is the relative energy of anti vs gauche conformers of butane?
110
Why is the anti conformer of butane more stable than gauche?
111
What are the two eclipsed conformers of butane?
112
Which butane conformer is the least stable and why?
113
What are the dihedral angles between CH₃ groups in each conformer of butane?
114
What type of strain is present in the synperiplanar conformer?
115
How do you draw conformers along any specified C–C bond?
116
How can Newman projections be used to visualise conformers in alkanes beyond ethane and butane?
117
How can you calculate the energy of a conformer from its Newman projection?
118
How do you compare the energies of different conformers?
119
How can you predict the most and least stable conformer of a molecule?
120
What kind of interactions contribute to steric strain in conformers?
121
What is a stereoisomer?
122
What makes a carbon atom chiral?
123
What is a stereogenic centre?
124
What does it mean for a molecule to be chiral?
125
What is the difference between chiral and achiral molecules?
126
Why is chirality important in biological systems?
127
How do enantiomers behave differently in a chiral environment?
128
What is the "lock and key" model in the context of chirality?
129
Give examples of molecules with different effects depending on chirality.
130
What is a polarimeter?
131
What does a polarimeter measure?
132
What is optical rotation?
133
What is the formula for specific rotation?
134
In the equation [α]ᴅ = α / (l × c), what does each variable represent?
135
What is an enantiomer?
136
What is a racemate?
137
How do enantiomers affect plane-polarised light?
138
Why is a racemate optically inactive?
139
How can you experimentally determine if a compound is optically active?
140
What are the Cahn-Ingold-Prelog (CIP) priority rules?
141
How do you assign priorities to substituents around a chiral centre?
142
How do you determine the absolute configuration (R/S) of a chiral centre?
143
What is the R configuration?
144
What is the S configuration?
145
How do you use phantom atoms for double or triple bonds?
146
What should you do if two substituents are tied in atomic number?
147
What is a diastereoisomer?
148
How do diastereoisomers differ from enantiomers?
149
What is a meso compound?
150
How can a compound be achiral even if it has chiral centres?
151
How many stereoisomers are possible for a molecule with n chiral centres?
152
How do you assign absolute configurations to molecules with more than one chiral centre?
153
What is the relationship between molecules that differ at only one chiral centre?
154
How can you identify enantiomers among multiple stereoisomers?
155
How can you identify diastereomers among multiple stereoisomers?
156
What is the general formula for cycloalkanes?
157
What are the bond angles and strain characteristics of cyclopropane, cyclobutane, cyclopentane, and cyclohexane?
158
Why is cyclopropane considered the most strained cycloalkane?
159
What are banana bonds and how do they form in cyclopropane?
160
What types of ring strain affect cycloalkanes?
161
Which types of strain contribute to the instability of cyclopropane?
162
Why is cyclohexane the most stable cycloalkane?
163
What are the different conformations of cyclohexane?
164
Why is the chair conformation of cyclohexane more stable than the boat conformation?
165
How much more energy does the boat conformation have compared to the chair conformation?
166
What is a half-chair conformation and how stable is it?
167
What is a skew boat conformation and how does its stability compare to the chair and boat conformations?
168
What happens during a ring flip in cyclohexane?
169
What is the energy barrier for a cyclohexane ring flip?
170
What is the difference between axial and equatorial positions in cyclohexane?
171
Why does methylcyclohexane favor the equatorial conformation?
172
What is 1,3-diaxial strain and how does it affect conformational stability?
173
What is the strain energy of different substituents in the axial position of cyclohexane?
174
Why does tert-butylcyclohexane strongly favor the equatorial position?
175
How does cis-trans isomerism arise in cycloalkanes?
176
What stereochemical configurations correspond to cis and trans isomers in disubstituted cyclohexanes?
177
What is the most stable conformation for 1,2-disubstituted cyclohexanes (cis vs trans)?
178
What is the most stable conformation for 1,3-disubstituted cyclohexanes (cis vs trans)?
179
What is the most stable conformation for 1,4-disubstituted cyclohexanes (cis vs trans)?
180
How can you determine the most stable conformation of a disubstituted cyclohexane?
181
What is the structure of trans-decalin and can it undergo a ring flip?
182
What is the structure of cis-decalin and can it undergo a ring flip?
183
What is sp² hybridization and how does it relate to alkene carbon atoms?
184
How is a π-bond formed according to the valence bond model?
185
What is the structure of a double bond in terms of orbital overlap?
186
What are the key structural data (bond angles and lengths) for ethene?
187
What is geometric isomerism in alkenes and what causes it?
188
What are the IUPAC rules for naming alkenes?
189
What are the Cahn-Ingold-Prelog (CIP) rules for naming geometric isomers?
190
What are the types of polyenes?
191
How do you name simple polyenes?
192
What is the structure of benzene and what does resonance mean in this context?
193
How do you name simple monosubstituted benzenes?
194
How do you name disubstituted benzenes and assign ortho/meta/para positions?
195
How do you name polysubstituted benzenes using IUPAC rules?
196
What are the four structural requirements for aromaticity?
197
What is Hückel’s rule and how is it used to determine aromaticity?
198
What does it mean for a compound to be fully conjugated?
199
What is the hybridisation state of carbon atoms in an aromatic ring?
200
What geometry is associated with sp hybridisation?
201
How do two p-orbitals form two π bonds in a triple bond?
201
What is the hybridisation of carbon atoms in ethyne?
202
What kind of overlap forms a σ bond in a triple bond?
203
What is the bond angle in ethyne?
204
What are the bond lengths and bond strength in ethyne?
205
What are the IUPAC rules for naming alkynes?
206
What defines a primary, secondary, tertiary, and quaternary carbon atom?
207
What is a benzylic carbon?
208
What is an aryl carbon?
209
What is an allylic carbon?
210
What is a vinylic carbon?
211
What is the IUPAC name and structure of an alcohol?
212
What is the IUPAC name and structure of an ether?
213
What is the IUPAC name and structure of a thiol?
214
What is the IUPAC name and structure of an amine?
215
What is the IUPAC name and structure of an aldehyde?
216
What is the IUPAC name and structure of a ketone?
217
What is the IUPAC name and structure of a carboxylic acid?
218
What is the IUPAC name and structure of an ester?
219
What is the IUPAC name and structure of an amide?
220
What is the IUPAC name and structure of a nitrile?
221
What is the order of priority of functional groups in IUPAC nomenclature?
222
How is a carbonyl group formed according to the valence bond model?
223
Why is the carbon-oxygen double bond in a carbonyl group polarised?
224
What is the polarity of atoms in a carbonyl group?
225
What is electronegativity and how does it vary across the periodic table?
226
How does electronegativity difference affect bond polarity?
227
What is a dipole moment and what are its units?
228
How can you determine if a molecule has a net dipole moment?
229
What are the three main types of intermolecular forces?
230
How do instantaneous dipoles arise?
231
What is a dipole-dipole interaction?
232
What is hydrogen bonding and what conditions are required for it?
233
Why must an aromatic compound be planar and cyclic?
234
What is the significance of continuous p-orbitals in aromaticity?
235
Give examples of common aromatic compounds.
236
Why are some aromatic compounds carcinogenic after metabolism?
237
Name drugs that contain aromatic rings.
238
What molecular features can be visualised using AFM?
239
How is an sp hybrid orbital formed from s and p orbitals?
240
What is the geometry and bond angle of sp hybridised carbons?
241
What are the bond lengths and strength of the triple bond in alkynes?
242
Why don't alkynes exhibit geometric isomerism?
243
Name drugs that contain alkyne groups.
