It doesn't show the C or H, each "kink" represents a carbon and it is assumed to have the right number of hydrogens
New cards
7
What is stereoisomerism?
A type of isomerism in which molecules have the same molecular formula and atoms are bonded together in some order but arrangement of atoms is different
New cards
8
What are the 2 types of stereoisomerism?
Geometric and optical isomerism
New cards
9
Where does geometric isomerism occur?
In molecules containing C\=C or ring structure as there is no free rotation of groups of atoms around the double bond
New cards
10
What are the 2 types of geometric isomerism?
Cis and trans
New cards
11
What does cis mean?
The substituent groups are on the same side
New cards
12
What does trans mean?
The groups are on opposite sides
New cards
13
Which is more stable, cis or trans alkenes?
Trans
New cards
14
Why are trans alkenes more stable than cis?
Due to steric hindrance of 2 groups on the same side of C\=C.
New cards
15
Are cis and trans the same compounds? And what does this mean for their physical and chemical properties?
They are different compounds so have different physical and chemical properties
New cards
16
Why do trans isomers have a higher melting point and higher density?
They have a straighter molecule shape so can pack closer together. This leads to a higher density and stronger intermolecular forces between the molecules, resulting in more energy being required to overcome these forces
New cards
17
Are trans fats common in nature?
No
New cards
18
How are artificial trans fats formed?
When unsaturated oils undergo addition reactions with hydrogen to make them less unsaturated and more solid
New cards
19
What are the downsides to producing inactive drugs?
They waste materials, money and need higher dosage
New cards
20
Where does optical isomerism occur?
In chiral molecules where 4 different groups are arranged around a central carbon atom known as a chiral atom
New cards
21
What are optical isomers?
Non-superimposable mirror images of each other
New cards
22
How are optical isomers similar/ different form each other?
They have identical physical and chemical properties but different optical activities
New cards
23
How are optical activities measured?
Using a polarimeter
New cards
24
What is plane-polarised light?
Light travelling in only 1 plane
New cards
25
What do optical isomers do to plane polarised light?
Rotate plane polarise light through same angles but different directions
New cards
26
What does a clockwise rotation of plane polarised light mean?
It is dextrorotatory, the + isomer
New cards
27
What does an anti-clockwise rotation of plane polarised light mean?
It is levorotatory, the - isomer
New cards
28
What is a racemic mixture?
When there are equal quantities of the 2 optical isomers present
New cards
29
Do racemic mixtures have an effect on polarised light and why?
They do not since they are optically active
New cards
30
How does elemental microanalysis work?
A known mass of a compound is burned in excess oxygen to produce CO2, H2O, SO2, NOx. The mixture of gas is carried in a stream of helium over heated copper which reduces NOx to N. The mass of the remaining compounds can then be calculated
New cards
31
What information does mass spectroscopy give?
The molecular mass of a compound and structural fragments present in the compound
New cards
32
What is m/z ratio?
The mass to charge ratio of the fragment
New cards
33
What will the peak with the highest m/z ratio represent?
The un-fragemented parent molecule (which gives the molecular mass of the compound)
New cards
34
What is Infra-Red spectroscopy used for?
To identify certain functional groups in organic compounds
New cards
35
What does IR spectroscopy do to bonds?
Causes them to vibrate, stretch and bend.
New cards
36
What does the wavelength which affects the bonds depend on?
The type of bond present and atoms in these bonds
New cards
37
What does a wide peak suggest?
Hydrogen bonding
New cards
38
What is +H NMR spectroscopy?
Proton nuclear magnetic resonance
New cards
39
What can +H NMR spectroscopy give information of?
It can give information about different environment of hydrogen atoms in a molecule and about how many hydrogen atoms are in each of these environments
New cards
40
What do protons posses and what does this mean for the nucleus of hydrogen atoms?
A property called spin so the nucleus of hydrogen atoms behave like tiny magnets
New cards
41
What do nuclei do in a magnetic field?
Align themselves with the field
New cards
42
What will nuclei parallel to the magnetic field have?
Lower energies than those that oppose
New cards
43
What can energy in the form of radio waves be used for?
To change the hydrogen nuclei within the magnetic field from the lower state to a higher state
New cards
44
What does the energy difference depend on?
The environment the nuclei is in (electrons shield the nuclei from the magnetic field)
New cards
45
What happens when the nuclei fall back to a lower state?
Energy is emitted and can be detected which results in peaks called chemical shifts
New cards
46
What does the frequency of emitted radio waves tell us?
It gives us information on position of Hydrogen atoms in the molecule
New cards
47
What does the area under the peak correlate to?
The number of Hydrogen atoms in that environment
New cards
48
What is TMS used for?
A standard reference substance when running NMR spectroscopy
New cards
49
What is the chemical shift value of TMS?
0
New cards
50
What are the 2 types of +H NMR spectrum?
Low resolution and high resolution
New cards
51
Describe low resolution.
The chemical shift and area under the peak is interpreted
New cards
52
Describe high resolution.
Interactions with Hydrogen atoms on neighbouring Carbon atoms can result in splitting of peaks into multiplets
New cards
53
How can the number of peaks in a multiplet be calculated?
n +1, where n is the number of hydrogen atoms on neighbouring carbon atoms
New cards
54
What type of orbitals do electrons involved in bonding occupy?
Bonding molecular orbitals
New cards
55
Desire anti-bonding molecular orbitals.
They re usually empty unless the number of electrons available for bonding would violate the Pauli principle
New cards
56
What is the order of energy with the orbitals?
bonding molecular orbitals < atomic orbitals , anti bonding orbital (most energy)
New cards
57
What is the hydride ion?
H^-
New cards
58
Are hybrid orbitals degenerate?
Yes
New cards
59
What are π molecular orbitals/ π bonds?
Molecular orbitals that form by side-on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond
New cards
60
What is hybridisation?
The process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals
New cards
61
How do alkenes hybridise?
Their 2s orbitals and 3 2p orbitals of carbon hybridise to form 4 degenerate sp3 hybrid orbitals, which adopt a tetrahedral arrangement
New cards
62
How do the sp3 orbitals form σ bonds?
They overlap end-on with other atomic orbitals
New cards
63
Is the C-C in alkanes able to rotate freely?
Yes
New cards
64
What is the type of hybridisation in alkenes?
The 2s orbitals and 2 2p orbital hybridise to form 3 degenerate sp2 hybrid orbitals which adopt a trigonal planar arrangement
New cards
65
How do the sp2 orbitals form σ bonds?
They overlap end-on
New cards
66
What happens to the remaining unhybridised 2p orbital in alkenes?
It lies perpendicular to the axis of σ bond and they overlap side one to form π bonds
New cards
67
What does a C\=C consist of? (in terms of pi and sigma bonds)
1 σ + 1π bond
New cards
68
What is the type of hybridisation in benzene and other aromatic compounds?
sp2
New cards
69
How are benzene rings arranged?
6 carbon atoms are arranged cyclicly with σ bonds between carbon atoms
New cards
70
What do the unhybridised p orbitals do in benzene rings?
The overlap to form a π molecular system, perpendicular to the plane of π bonds
New cards
71
What is the type of hybridisation in alkynes?
2s and 2p orbitals of carbon hybridise to form 2 sp degenerate hybrid orbitals, adopting a linear arrangement
New cards
72
What happens to the unhybridised p orbitals in alkynes?
They overlap side on to form 2π bonds
New cards
73
What do the 2 hybrid sp orbitals in alkynes do?
Overlap end-on to form σ bonds
New cards
74
What does a C-C consist of? (in terms of π and σ bonds)
1 σ bond
New cards
75
What does a C≡C consist of? (in terms of π and σ bonds)
1 σ, 2 π bonds
New cards
76
What its energy form light used to do?
Promote electrons form bonding or non-bonding orbitals into the higher energy anti-bonding orbitals
New cards
77
What do σ and π orbitals contain?
Normal bonding pairs of electrons
New cards
78
What do non-bonding orbitals contain?
Lone pairs of electrons
New cards
79
What do σ* and π* anti-bonding orbitals contain?
They are normally empty
New cards
80
How do electrons fill the orbitals?
They fill bonding molecular orbitals, leaving the anti-bonding orbitals unfilled
New cards
81
What is the Highest Occupied Molecular Orbital (HOMO)?
The highest bonding molecular orbital containing electrons
New cards
82
What is the Lowest Unoccupied Molecular Orbital (LUMO)?
The lowest anti-bonding molecular orbital
New cards
83
What can cause electrons to be promoted from HOMO to LUMO?
Absorption of electromagnetic energy
New cards
84
Why do most organic molecules appear colourless?
Because the energy difference between HOMO and LUMO is relatively large which results in the absorption of light from the ultraviolet region of the electromagnetic spectrum
New cards
85
Why are some organic molecules coloured?
Dueto a conjugated system
New cards
86
What does a conjugated system contain?
Delocalised electrons spread over a number of atoms (alternating σ and π bonds)
New cards
87
Are benzene rings conjugated and why/ why not?
Yes because of the delocalised electrons
New cards
88
What are chromophores?
A group of atoms within a molecule that is responsive for absorption of light in the visible region the spectrum
New cards
89
When can light be absorbed?
When electrons in a chromophore are promoted from the HOMO to the LUMO
New cards
90
Where do chromophores exist?
In molecules containing a conjugated system
New cards
91
What is a conjugated system?
A system of adjacent unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of carbon atoms
New cards
92
What does more atoms in the conjugated system mean?
A smaller gap between HOMO and LUMO
New cards
93
When frequency of light decreases, what happens to wavelength and energy?
Wavelength gets longer, energy decreases
New cards
94
When will the compound exhibit colour?
When the wavelength of light absorbed is in the visible region, the complementary colour is exhibited
New cards
95
What does a single-headed curly arrow mean?
It shows movement of a single electron
New cards
96
What does a double-headed curly arrow mean?
It shows the movement of a pair of electrons
New cards
97
Where should the arrow start and finish?
It should start at the origin of electrons and finish at the destination of electrons
New cards
98
What does it mean if an arrow points to a space between 2 atoms?
It indicates that a coolant bond will be formed between them
New cards
99
Describe what happens to bonds during an organic reaction.
Bonds in the reactant molecules are broken (bond fission) and bonds in the product molecules are being made
Studied by 11 people
