block 1 chem110

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Chem110 Notes

Block 1: Unit 1

Differences between ionic and covalent bonding

Ionic bond

Covalent bonding

o Bonds

End on overlap of AO

σ bond

Sideways overlap of AO

π bond

o π bond weaker than σ bond

addition reaction occur in π bond

o Tetravalent

Carbon forms 4 bonds in neutral compound

o Single bond

σ ( 2 electrons)

o Double bond

σ +π (4 electrons)

o Triple bond

σ+ 2 π (6 electrons)

o Valence: number of bonds to an atom in a stable neutral (uncharged) molecule.

Carbon=4

Nitrogen=3

Oxygen/sulphur=2

Halogen=1

o Single bond>double bond>triple bond (decrease bond length, increase bond

number, increase number of electrons)

Rotation

Not possible in a C-C multiple bond.

Possible in C-C single bond (not in rings)

Bonding in organic compounds

Completely filled outer shell of electrons is a stable arrangement

Atoms

o Loss or gain electrons to achieve completely filled outer shell

Form ions o Share electrons

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By atomic orbital (AO) overlap – covalent bonds

Covalent bond

Bonds

o End on overlap of AO σ bond

o Sideways overlap of AO

π bond

π bond weaker than σ bond

o addition reaction occur in π bond

Tetravalent

o Carbon forms 4 bonds in neutral compound

Single bond

o σ ( 2 electrons)

Double bond

o σ +π (4 electrons)

Triple bond

o σ+ 2 π (6 electrons)

Valence: number of bonds to an atom in a stable neutral (uncharged) molecule.

o Carbon=4

o Nitrogen=3

o Oxygen/sulphur=2

o Halogen=1

Single bond>double bond>triple bond (decrease bond length, increase bond number,

increase number of electrons)

Rotation

Not possible in a C-C multiple bond.

Possible in C-C single bond (not in rings)

Functional groups

Is an atom (not H) or a group of atoms (not alkyl) attached to carbon(s) in an organiccompound. It can also be a carbon to carbon multiple bond, which is part of the

molecular framework.

Where reactions usually happen (hydrocarbon chain quite unreactive)

Geometry about carbon

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Notation (hybridization state)

Non-hybridised state

sp3

o s+p+p+p

o 4 equivalent bonds

sp2 o s+p+p

o 3 sp2 orbitals + p

sp

o s+p

o 2 sp orbitals +2p

Nomenclature

Meth(1), Eth(2), Prop(3), But(4), Pent(5), Hex(6), Hept(7), Oct(8), Non(9), Dec(10)

Longest straight chain is the parent nameo *name must contain C=C for alkene

Identify and give lowest possible sum of numbers for substituents (alkyl, alkoxy,

chloro, etc)

Prefix contains the number of substituents

o *add cyclo- for cycloalkanes

C=C + oxygen containing functional group

o *Alk-#-en

Primary, secondary, tertiary alcohol, amino

Aliphatic: group not attached to aromatic ring. Thiol: alkane thiol, thioether

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Aromatic

Mono-substituted= substituent + benzene

Di-substituted

o Ortho (O-1,2), Meta (M-1,3), Para (P-1,4)

o *Use lowest sum of numbers.

Block 1: Unit 2

Constitutional isomerism

Isomer

o Same molecular formula Same molecular formula but different atom to atom bonding sequence.

Types

o Position of functional group

o Type of functional group (alcohol vs ether)

Double bond equivalents (DBE)

o Degree of unsaturation

o DBE= # π + # rings (even rings containing O)

o *N1= hydrogen of halogen

o

Stereoisomerism

Same molecular formula, same atom to atom bonding sequence, but different

arrangement of their atoms in space.

Conformational

o Interconvert by rotation about C-C single bond

o Interconversion requires no bond breaking

o Conformation: the particular shape the molecule adopts as a result of rotation

about bonds.o 0= methyl group

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Main example: Cyclohexane

o Chair Each carbons wants 109.5 °

Not planar

2 distinct sets of bonds

Lowest energy conformer

Ring flip: all axial groups become equatorial and vice versa.

o Boat

No axial/equatorial classification

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o Substituted Steric interference: unfavourable interaction between groups

Favoured conformer

Largest atom/ groups in equatorial position.

Not possible to have all substituents in equatorial position

Largest groups in axial is more stable than both in equatorial position

Configurational

o Can only interconvert if a covalent bond is broken and reformed. o Cis-Trans isomers

Atoms/groups held in different positions by ring or C=C

*1 atoms/group common to both sp2/sp3

o E-Z system

Developed by Cahn, Ingold, Prelog

1. Atom with higher atomic number directly attached to carbon has

higher priority

2. If directly attached atom is the same go to the next atom until priority

can be assigned at the first point of difference.

Cis-trans in chair conformer

Draw the conformer to if

substituents are cis or trans to

each other

E.g. both axial= trans

Left is a general formula for

substituents in the same

orientation

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3. Groups with double bonds are considered as being bonded to 2 of the

atoms by single bonds (e.g C=C has higher priority to C-C)

Z (zusammen)

o 2 higher (Hi) priority groups on the same side.

E (entgegen)

o Hi on opposite sizes

Enantiomer

Contains an asymmetric carbon with 4 different groups.

Molecule cannot be superimposed on it mirror image.

*Enzymes have enantiomers at its active site (specific)

Chiral: molecule contains stereogenic centre

Achiral

o has 2 identical atoms/groupso plane of symmetry

o superimposable on its mirror image

Enantiomer differs in their interaction with a chiral medium/reagent (e.g plane

polarized light [PPL])

o Rotates to right

Dextrorotatory (+)

o Rotates to left

Laevorotatory (-)

Racemic mixture

o Equal amount of two enantiomers

o Has zero rotation of PPL

*sign, magnitude of rotation not convey configuration

Configuration conveyed by

o Fischer projection

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o Steering wheel approach

Diastereomers: stereoisomers that have a non-mirror image relationship.

Block 1: Unit 3

Physical properties

Properties in relation to structure

Molecular size/ molar mass

o Increase molecular size increases boiling point

Due to increased van der Waals forces

Molecular shape

o Increasing branching decreases boiling point

Functional groups

o Degree of unsaturation Little effect on boiling point

o Types (boiling point lowest to highest)

Alkanes-ether-halogeno-ketone-aldehyde-amino-alcohol-carboxylic

acid

Assume similar molar mass

Boiling point increases due to more polar bonds increasing

intermolecular interactions

Bond polarity

Overall polarity of a molecule depends on

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o Size of hydrocarbon portion

o Nature of functional group

In organic molecules most bonds are covalent

Bonds range from strictly covalent (C-C) to polar bonds (O-H)

Polar bondso Electrons comprising bonds are not equally shared between bonded atom

One bonded atom carries

Partial positive charge (δ+)

Partial negative charge (δ-)

*Bond polarity measures the difference in electronegativity of bonded atoms

Electronegativity

Measure of ability of a bonded atom to attract electrons to itself

*Electrostatic potential maps

Increase electronegativity of bonded atoms increase polarity of bond

Partial negative charge

o More electronegative atom of the bond

Partial positive charge

o More electropositive atom of the bond

Trends

o Electronegativity C>H>B

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Hydrogen bonding

Presence of O-H group

Lesser extent in N-H C=O more polar than C-O

o More electrons available in bond

o Mobility of π electrons

More H-bond

o Increase boling point

o Increase water solubility

Ionic bonds

More polar than H-bonds

Present in amine/ carboxylic acid salt

Water solubility

Functional group Relative polarity Water solubility

Hydrocarbon, halide, ether Low Insoluble

Ester, aldehydes, ketones,

amides, amines, alcohol,

acids

Intermediate Soluble up to 5 carbons

Amine/ carboxylic acid salts High Soluble up to 7 carbons

*Increasing hydrocarbon portion decreases water solubility

o Reverse in non-polar solvents

Chromatography

Polar

o Solute is more strongly attracted to polar stationary phase

Move slowly

Non-polar

o Solute is more soluble in mobile phage (relatively non-polar)

Move rapidly

Reaction classification

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Substitution

o One atom or group is replaced by another

o Same DBE

Addition

o 2 atoms or groups added to a molecule with double/triple bond

o Decrease DBE

o More saturated

Elimination

o 2 or more groups removed from a molecule

o Increase DBE

o Less saturated

Electron movement

Homolytic

o Homolysis

o symmetrical

o One electron of pair in the bond ends up on each of the atoms that were

bonded

o A-B →A∙ + B∙

o Form free radicals

Neutral species with unpaired electrons

E.g. carbon centred free radical

Heterolytic

o Heterolysis

o Unsymmetrical

o Both electrons of bonding pair end up on one of the bonded atoms

o Direction of electron pair movement depend on relative electronegativity of

bonded atoms

o Electron move toward more electronegative atom of bondo Carbocation or carbanion formed

Formal charges

Lose ownership of shared bonding electrons

o One unit of charge more positive

Gain ownership of shared bonding electrons

o One unit of charge more negative

Carbocation

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Stability

o Carbocation attached to aryl ring>3°>2 °>1 °> methyl

Lower energy intermediate is favoured

Charge delocalisation over more atoms

o Lower energy

o More stable

Covalent bond formation

Heterogenesis

o C+ + A- = C-A

o C- + A+ = C-A

o Polar reactions

Nucleophiles

Electron rich

Provide an electron pair to an electron deficient centre to forma new bond

N for Negative

π electrons

Electrophiles

Electron deficient

Accept electron pair to form a new bond

Positive atoms

Electropositive atom in polar bond

Homogenesis

o C∙ + A∙ = C-A

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o Non-polar reaction

Bond breaking

Homolytic

Bond making

Homogenic

block 1 chem110

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