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Chemistry 10003 > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

1
Q

What are the spatial orientation of orbitals?

A

1s and 2s = round (yellow cloud is positive, blue cloud of negative)
2px = horizontal axis
2py = vertical axis
2pz = diagonal axis facing towards us

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2
Q

What is ground state electronic configuration?

A 
Arrangement of electrons around the nucleus of an atom with lower energy levels
1s1 
1 = which shell
s = which orbital
1 (superscript) = how many electrons
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3
Q

What bond is present in covalent bonds

A

Sigma bond is present when a pair of elements share their electrons
Formed by the head on overlap of orbitals (can be s or p orbitals)

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4
Q

Covalent bonding between H2 - energy, distance

A 
Energy = 436 kJ/mol
Distance = 0.74 angstroms
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5
Q

Definition of hybridisation

A

Mixing of different (similarly energised) orbitals to create a set of new orbitals that have the same energy

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6
Q

Example of hybridisation in alkanes

A

Hybrid orbitals are present in methane
C-H bonds become all the same due to hybridisation
1 x s + 3 x p orbitals = 4 sp3 orbitals
All carbons in alkanes are sp3 hybridised

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7
Q

Shape of sp3 hybridised orbitals

A

Shape of orbitals becomes all different
Instead of two equal shaped ovals, one becomes larger and other becomes smaller and the oriental shape is all at different angles.
The different orientation is due to minimising the repulsion between them
Most stable arrangement is at tetrahedral (angle is 109.5) –> the 4 electron pairs are as far away from each other

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8
Q

Definition of angstrom

A

Unit to measure bond length

Is approximately equal to 10^-10 metres

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9
Q

Sigma bond in hybridised orbitals in methane

A

sp3 hybridised orbitals and overlap and form a sigma bond
has a circular cross section
1s orbital of hydrogen overlaps sp3 orbitals to form a single C-H bond
Length of C-H bond = 1.09 angstroms
Energy of C-H bond = 349 kJ/mol

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10
Q

Structure of ethane

A

Has 2x set of sp3 hybridised orbitals
Sigma bond (circular cross section) between C-C
Sigma bond between C-H
C-C-H bond angle = 111.2
C-C bond length = 1.54 angstroms
C-C energy bond = 377 kJ/mol (easier to break compared to C-H bond)

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11
Q

Formula of alkanes

A

CnH(2n+2)
Alkanes are compounds of only carbon and hydrogen, with each carbon has 4 tetrahedrally arranged sigma bonds = saturated hydrocarbons

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12
Q

Substituent names

A 
Methyl - CH3
Ethyl - CH2CH3
Propyl - CH2CH2CH3
Isopropyl - CH(CH3)2
tert-butyl- C(CH3)3

di, tri, tetra, penta - is used for substituents and do not count for alphabetical order

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13
Q

How many isomers does hexane and decane have?

A

Hexane has 5 isomers

Decane has 75 isomers

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14
Q

Prime example of alkanes

A

Octane is used as petrol for cars
96 and 98 fuel are just structural isomers of octane
The more branches the structure has = more volatile = more energy produced

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15
Q

IUPAC naming in tricky situations

A

In very long/branched alkanes, always start at the carbon that has branched off points in lowest number (e.g. CH3 group on second carbon rather than on 4th carbon)

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16
Q

Haloalkanes (alkyl halides)

A

Instead of hydrogen atom forming a sigma bond, a halide can form a sigma bond with carbon

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17
Q

Difference between fluoromethane and iodomethane?

A

C-F bond length and strength = 1.39 angstroms and 360 kJ/mol
C-I bond length and strength = 2.14 angstroms and 239 kJ/mol

much longer and weaker bond in iodine due to larger atom present causing a stronger repulsion
iodomethane would be easier to break and undergo chemical reactions

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18
Q

Definition of conformational isomers (stereoisomers)

A

Isomers that have same molecular formula and connectivity of atoms but differ by C-C bond rotation

Carbon atom have ‘free rotatation’ due to sigma bond

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19
Q

Definition of stereoisomers

A

Isomers that have same molecular formula and sequence of bonded atoms but different spatial orientations

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20
Q

Newman projects

A

Used frequently in conformational stereoisomerism
Diagram of molecule from straight eye view

Front carbon = proximal
Back carbon = distal

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21
Q

Conformational isomers of ethane

A

In newman projections, angle between H-H is 60 degrees (dihedral angle)

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22
Q

Different types of conformational isomerism (using ethane as an example)

A

Molecules change energy as the carbon rotates

Staggered is most stable (all angles are 60 degrees between H-H)
Eclipsed is the least stable (hydrogen atoms are on top of each other, in real space model, hydrogen atoms would be too close) (in eclipsed, dihedral angle becomes 120 degrees)
Eclipsed formation has 12 kJ/mol higher than staggered due to torsional strains

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23
Q

Types of strains present in conformational isomerism

A

Torsional strain = strains due to bonds interacting with each other
Steric strain = strains due to interaction between atoms, clouds and their nuclei becoming too close

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24
Q

Conformational isomers of butane

A

Staggered anti = most stable conformation (methyl groups are 180 degrees away from each other (dihedral angle)

Staggered gauche = When front carbon rotates 120 degrees, methyl group is next to each other (dihedral angle = 60 degrees)
3.8 kJ/mol higher than staggered anti

2 eclipsed formation = methyl group on top of hydrogen + methyl group on top of methyl group

CH3 + H = 16 kJ/mol higher in energy
CH3 + CH3 = 19 kJ/mol higher in energy, is the least stable, has steric and torsional strain

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25
Q

Reason for conformational isomers

A

Alkanes at room temperature can freely rotate about their carbon-carbon bond

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26
Q

Definition of chiral

A

Mirror image is not identical (non-superimposable) and can rotate plane of polarised light

Carbon with 4 different substituent groups attached is called asymmetric centre/stereogenic centre

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27
Q

Definition of enantiomers (optical isomers)

A

Stereoisomers that have same physical and chemical properties but react differently to a plane of polarised light and in chiral environments

Pair of non-superimposable mirror images

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28
Q

Definition of racemate

A

1:1 ratio mix of enantiomers

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29
Q

What is [a]d

A

specific rotation of a molecule (with enantiomers, they are always opposite)

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30
Q

Equation for [a]d

A

(a) / (l x c)

a = angle through polarised light is rotated
l = length path 
c = concentration
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31
Q

Naming enantiomers (asymmetric carbon)

A
  • determine priority of four substituents (atomic number) of atom DIRECTLY attached to asymmetric carbon
  • determine order
R = clockwise
S= anticlockwise

(ensure lowest priorty atom is NOT facing towards us)

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32
Q

Definition of diastereoisomers

A

Stereoisomers that are not enantiomers

non-superimposable images but are NOT mirror images
have different physical + chemical properties

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33
Q

Formula for number of stereoisomers

A

2^n

n= number of asymmetric centres

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34
Q

Definition of meso compounds

A

Exceptions to stereoisomers (with 2 or more asymmetric carbons) that are NOT CHIRAL

achiral-superimposable mirror image

(mirror images are superimposable, look for plane of symmetry)
e.g. 2,3-dibromobutane

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35
Q

Cycloalkane formula

A

(CH2)n

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36
Q

Angles in cycloalkanes

A

Cyclopropane = 60 degrees
•deviated from sp3 109.5 (ring strain = very unstable as c-c bond is too close)

Cyclobutane = 90 degrees
Cyclopentane = 108 degrees 
Cyclohexane = 120 degrees (if flat plane)
37
Q

Sigma bonds in cyclopropane

A

Sigma bonds are bent in cyclopropane (‘banana bonds’)
this is due to small angles and causes ring strain (due to abnormal angles)

cyclopropane has highest strain
cyclohexane has 120 degrees which is higher than tetrahedral angle thus ring strain is least (to reduce strain, it conforms)

38
Q

Conformation of cyclohexane

A

reduces angle strain and torsional strain (strains from bonds)

planar ring of cyclohexane ‘puckers’
one carbon moves above the plane and the carbon on the opposite side moves down the plane = CHAIR CONFORMER (most preferred)

39
Q

Chair conformation of cyclohexane

A

C-C-C bond angle is 111 degrees (closer to tetrahedral angle)

6 axial and 6 equatorial hydrogens that rapidly interchange with each other at room temperature (ring inversion/flip)

40
Q

Type of C-H bonds in rings

A

Axial bonds = hydrogen bonds are vertical (up and down)

Equatorial bonds = hydrogens point outwards from ring (sideways)

41
Q

Boat conformation of cyclohexane

A

29 kJ/mol more than chair conformation

has steric and torsional strain

42
Q

Conformations of substituted cycloalkanes

A

Axial position of substituent is less preferred due to higher energy and less stability (more steric and torsional strain)

e.g. methylcyclohexane
•methyl group can be equatorial or axial
•methyl group at equitorial is more abundant due to lowest energy
•methyl group at axial = 7.6 kJ/mol more (when rotating, CH3 group will collide with neighbouring hydrogens)
1,3-diaxial interactions (steric interaction)

43
Q

Conformations of tert-butylcyclohexane

A

due to larger substituent group, likelihood of tert- to be at equitorial is much higher than methylcyclohexane

tert- at axial = 22.8 kJ/mol more in energy than equitorial (1,3-diaxial steric interaction)

44
Q

Cis-Trans Isomerism of DISUBSTITUTED cycloalkanes (configurrational isomers)

A

C=C bonds do not rotate as freely meaning the groups attached retain their relative orientation

Cis = groups are on same face
Trans = groups are on opposite face
(FLAT PLANE)

45
Q

Axial and Equatorial relationships in Cis- and Trans-

A

1,2-Cis = ax,eq / eq, ax

1,2-Trans = ax,ax / eq,eq

1,3-Cis = ax,ax / eq,eq

1,3-Trans = ax,eq / eq, ax

1,4-Cis = ax,eq / eq, ax

1,4-Trans = ax,ax / eq,eq

46
Q

Cis- and Trans- Isomerism relating to Ax and Eq

A

If both isomers have opposite groups (one Ax and Eq), then smaller gorup MUST BE AXIAL

47
Q

Cycloalkanes nomenclature

A

Find parent ring (largest ring)

Place highest priorty substituent at C1 and number so second substituent is lowest number

48
Q

Polycylic compounds

A

More than 1 cycloalkanes

Cis and Trans decalin = fused cyclohexanes

49
Q

Exception to cis and trans decalin

A

Trans decalin, hydrogens (Axial) can not undergo ring flip and become equatorial

Molecule will rip apart

e.g. trans-decalin is present in cholesterol (making it rigid + hard)

50
Q

Alkenes orbitals

A

sp2 hybridised

1 x s + 2 x p orbitals = 3 sp2 hybrid
(one 2p orbital is left to be normal)

Trigonal planar (120 degrees between hybrid orbitals)

3 sp2 hybrid orbitals are diagonal and horizontal + p orbital which is vertical

51
Q

Alkenes bonding

A

sp2 orbital overlaps head on to form sigma bond that has circular cross section

remaining sp2 orbitals bonds with 1s orbital of hydrogen atoms

p orbital sideways overlap forming a pi bond (restricting carbon-carbon rotation as pi bond must be broken to rotate) (less efficient overlap)

52
Q

Geometric Isomerism (E-Z , alkenes)

A

2 different substituent groups on each side of C=C bond

E-Z notation

E = groups are on opposite sides
Z = groups are on same side
53
Q

Polyenes

A

Molecules with more than one double bond

Cummulated = double-double allenes

Conjugated = double-single-double

Isolated = double-single-single-

(adiene) = ending of nomenclature

54
Q

Delocalisation of rings

A

Delocalization of electrons occur in pi- clouds

In conjugated systems, p orbitals are able to form pi bonds from sideways overlapping (over single bond through the pi-clouds)

Electrons in pi-cloud are ‘spread out’ bringing greater attraction and stabilisation

55
Q

Example of E and Z isomerism

A

E-Z isomerism is found in vision

Rhodopsin (Z) and Metarhodopsin II (E) are isomers of each other

Light causes change in shape (breaks pi bonds causing the bonds to rotate rapidly) (double bonds reform and shape changes) sending a nerve impulse through optic nerve which is detected by brain
Causes a image perceive

56
Q

Definition of RESONANCE STABILISATION

A

stabilisation of a ring due to delicalised electrons in pi-clouds

57
Q

Benzene stabilisation

A

Benzene is very stable and not reactive due to overlapping p orbitals (pi clouds and continuous overlapping)

Electrons are no longer isolated between two single carbon atoms in double bonds

Electrons are delocalized all over the whole molecule

Every carbon atom in benzene is sp2 hybridised and has trigonal planar geometry

58
Q

Evidence of resonance in benzene

A

Bond length of C-C is 1.39 angstroms (in between a single and double bond)

Strength of bond is in between single and double bond as well

59
Q

Nomenclature of Monosubstituted Benzenes

A

Halogen group (e.g. bromine) = Bromobenzene

Methyl = Toluene

Alcohol (OH) = Phenol

Amine (NH2) = Aniline

60
Q

Nomenclature of Dsubstituted Benzenes

A

1,2 = ortho OR o-

1,3 = meta OR m-

1,4 = para OR p-

61
Q

Nomenclature of benzenes with more than 2 substituents

A
  1. Number the ring to give substituents lowest numbers
  2. Name substituents alphabetically

IF CARBON CHAIN IS LONGER THAN 6, BENZENE BECOMES SUBSTITUENT = phenyl

62
Q

Nomenclature with several rings

A

2 benzene rings joined by a single bond = biphenyl

2 or more benzene rings sharing 2 carbon atoms = polynuclear aromatic hydrocarbons

63
Q

Requirements of aromatic compounds

A
  • planar
  • cyclic
  • conjugated
  • follow Huckel’s rule (aromatic and anti-aromatic)
64
Q

Huckel’s Rule

A

Aromatic = 4n + 2 pi electrons
(2, 6, 10, 14, 18, 22)

Anti aromatic = 4n pi electrons
(0, 4, 8, 12, 16, 20)

65
Q

Usage of Atomic Force Microscopy (AFM)

A
  • very high resolution type of scanning probe
  • demonstrated resolution on the order of fractions of a nanometer

can see actual outline/shape of molecule

66
Q

Orbit hybridisation of Alkynes

A

Triple carbon-carbon bonds
•2s orbital + 2p orbital = 2 sp hybrid orbitals
•sp hybridised
•angle between sp hybrid orbitals is 180 degrees
•two p orbitals are left in original orientation (py and pz)

  • hybrid orbitals overlap and form a sigma bond (linear bond)
  • P orbitals that are perpendicular form pi bonds (2 pi bonds and pi clouds)
67
Q

Geometric isomerism of alkynes

A

NO GEOMETRIC ISOMERS POSSIBLE FOR ALKYNES

68
Q

Nomenclature of alkynes

A
  • triple bond at end of chain = terminal alkyne
  • triple bond in middle of chain = internal alkyne
  • suffix = ‘yne’
69
Q

Types of carbon atoms

A 
Primary = bonded to 1 other carbon atom
Secondary = bonded to 2 other carbon atoms
Tertiary = bonded to 3 other carbon atoms
Quaternary = bonded to 4 other carbon atoms
  • Benzylic carbon = sp3 hybridised carbon attached to benzene
  • Aryl carbon = sp2 hybridised carbon in aromatic structure
  • Vinylic carbon = sp2 hybridised carbon in a double bond (not aromatic structure)
  • Allylic carbon = sp3 hybridised carbon that is lone, attached to a vinylic carbon
70
Q

Functional group: Alcohol

A
  • oxygen is sp3 hybridised (tetrahedral)
  • oxygen has 6 valence electrons forming 2 covalent bonds
  • suffix = ‘ol’
  • prefix = ‘hydroxy’
71
Q

Functional group: Ethers

A
  • suffix = ‘ane’
  • prefix = ‘alkoxy’
  • oxygen atom bonded to 2 other carbons (middle of chain)
72
Q

Functional group: Thiols

A
  • suffix = ‘thiol’
  • prefix = ‘mercapto-‘
  • like an alcohol, but oxygen is replaced by SULFUR (-SH)
  • sp3 hybridised
73
Q

Functional group: Amines

A
  • suffix = ‘-amine’
  • prefix = ‘amino-‘
  • primary amine, secondary amine, tertiary amine (depends on how many carbons it is bonded to)
  • nitrogen is sp3 hybridised, lone pair occupies corner of tetrahedral (108 degrees)
74
Q

Functional group: Carbonyl (C=O)

A
  • polar molecule due to oxygen’s electronegativity (electrons closer to oxygen)
  • oxygen and carbon are both sp2 hybridised
  • both are trigonal planar (geometry)
75
Q

Functional group: Aldehyde

A
  • suffix = ‘al’ and ‘carbaldehyde’

* carbonyl group at end of chain

76
Q

Functional group: Ketone

A
  • suffix = ‘one’
  • prefix = ‘oxo’
  • carbonyl group attached to two c’s (not at end of chain)
77
Q

Functional group: Carboxylic acid (highest priority)

A
  • suffix = ‘oic acid’
  • prefix = ‘carboxy-‘
  • oxygens are sp2 and sp3 hybridised
78
Q

Functional group: Esters (second priority)

A
  • suffix = alcohol ‘yl’ and acid ‘oate’

* derrived from carboxylic acid + alcohol

79
Q

Functional group: Amides (third priority)

A
  • suffix = ‘amide’, ‘anamide’
  • C=O bond connected to nitrogen
  • primary amide = 2 hydrogens bonded
  • secondary amide = 1 hydrogen bonded
  • tertiary amide = no hydrogens bonded
80
Q

Functional group: Nitriles

A
  • suffix = ‘nitrile’
  • C≡N bond
  • sp orbital of carbon and nitrogen overlap forming sigma bonds
  • pi bonds (p orbitals)
  • linear shape (180 degrees)
81
Q

Combustion Analysis (analytical technique)

A

Combustion process creating carbon dioxide and water as a product (complete combustion)
-Allows percentage of elements in compound to be calculated (e.g. empirical formula, % of elements)

Incomplete combustion produces carbon dioxide, carbon monoxide and water

82
Q

Mass Spectrometry (analytical technique)

A
  • uses UV light
  • determines molecular mass of a sample
  • very sensitive technique, only needing small amount of sample (tears apart sample)
  • m/z value = mass of fragment/sample
  • M+ (largest weight sample) = molecular mass
  • base peak = tallest peak

process:
ionisation = molecule is bombarded with high energy electrons causing an electron to be knocked off sample
sample becomes positively charged
M+· –> M+ + fragment (radical)
forms a radical cation which undergoes fragmentation forming a radical and a carbocation (sample that gets detected)

acceleration
deflection
detection

83
Q

Mass Spectrometry (small line indicates?)

A

Small peak above the M+ is a [M+1]^+ ion due to carbon-13
(it is an isotope that is 1% of all carbon-12)

To calculate chance of having C13 =
Multiply the number of carbons by 1.1

84
Q

Ultraviolet Spectroscopy (analytical technique)

A

-usage of electromagnetic radiation (UV light + visible wavelength) where material absorbs different wavelengths determining structural elements of sample

85
Q

Infrared Spectroscopy (analytical technique)

A
  • use of infrared light where sample absorbs wavelengths to determine functional groups present
  • bonds in molecules are the ones to absorb wavelengths
  • bonds either stretch or bend when absorbing wavelength allowing this to be detected
  • far left hand side = N-H, O-H, C-H (2600-4000 cm-1)
  • middle left = C≡N, C≡C (2300-2100 cm-1)
  • middle right = C=O, C=N, C=C (1800-1540 cm-1)
  • far right = fingerprint region (absorption of many different wavelengths)
86
Q

Nuclear Magnetic Resonance Spectroscopy (NMR)

A
  • technique to determine connectivity of hydrogens and carbon13 in a sample + able to look at nuclei of a sample through absorbtion of wavelengths (radio frequency)
  • Tetramethylsilane (TMS) is used as a base comparison located at 0 ppm
  • Chemical shift = resonant frequency of a nucleus relative to a standard in magnetic field (TMS)
  • depends on magnetic spin and magnetic moment of the nucleus (different nucleus have different magnetic moments)
  • NMR uses very strong magnetic field where atoms will align with field of against
  • energy that is absorbed presents an NMR signal

Carbon13 and Proton NMR

87
Q

Carbon 13 NMR technique

A

200-0 ppm is for 13C NMR spectrum

  • number of lines in 13C represents number of carbons in sample
  • if number of lines is less, indicates there is some degree of symmetry
88
Q

Proton NMR Technique

A

10-0 ppm is for H NMR spectrum
number of protons in sample - given by integration line (measure heights and get ratio)
number of lines in a signal = shows number of protons nearby (within 3 bonds or less)

follows Resonance Coupling = N + 1 rule
N = nuclei present in adjacent carbons (hydrogens)
Final number/ratio is structured by Pascal’s Triangle (e.g. triplet = 1:3:3:1)

1 - singlet
2 - doublet
3 - triplet
4 - quartet

Proton coupling can occur for 13C (determines how many hydrogens are connected to carbon) but it is very noisy: use 13C DEPT spectra
DEPT-90 = shows C-H
DEPT-135 = shows C-H, CH3 and CH2 is inverted (negative)

89
Q

X-Ray Diffractometry (analytical technique)

A
  • uses x-ray range of wavelengths
  • allows structure to be determined (exact location of atoms in 3d space)
  • must be crystalline structure

Chemistry 10003 (3 decks)

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