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Medicinal Chemistry > Functional group chemistry > Flashcards

Functional group chemistry Flashcards

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1
Q

List the functional groups in increasing oxidation levels

A
  • The alkane oxidation level
  • The alcohol oxidation level
  • The aldehyde oxidation level
  • The carboxylic oxidation level
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2
Q

What are alkanes known as and why?

A

Paraffins due to unreactivity

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3
Q

State three properties of alkanes.

A
  • Poorly reactive with ionic or polar substances
  • Inert to acids and bases
  • Virtually insoluble in water
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4
Q

How are alkanes isolated?

A

From petroleum through distillation

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5
Q

Describe the melting point of alkanes.

A

Boiling points and melting points increase with the size of the alkane

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6
Q

Describe the forces between molecules in alkanes

A

Weak - temporary dipoles , dispersion

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7
Q

What are molecules coated with?

A

A layer of electrons which occupy bonding and maybe non-bonding orbitals - as a result they are negatively charged (molecules repel each other)

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8
Q

When do reactions occur?

A

If a pair of molecules have enough energy to overcome the superficial repulsion

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9
Q

Define activation energy

A

The minimum energy required to react

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10
Q

What brings molecules together?

A

Charge attraction or orbital overlap

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11
Q

What is the more common cause of organic reaction?

A

The attraction between a charged reagent ( a cation or anion) and an organic compound that both possess a dipole.

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12
Q

Define electrophile.

A

Electron acceptors

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13
Q

Define nucleophile

A

Electron donor

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14
Q

How do we identify nucleophiles?

A
  • They are either negatively charged or neutral species with a pair of electrons in a high energy orbital.
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15
Q

What is the most common type of nucleophile?

A

Has a non-bonding lone pair of electrons

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16
Q

How do we identify electrophiles?

A
  • They are neutral or positively charged species with an empty atomic orbital or a low-energy anti-bonding orbital that can easily accept electrons
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17
Q

Describe SN1 and SN2 reactions

A
  • Both can predominate
  • Use kinetic evidence to explain the mechanisms
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18
Q

What does the rate of an Sn2 reaction depend on?

A
  • The nucleophile
  • The carbon skeleton
  • The leaving group
  • Temperature and solvent
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19
Q

What does the rate of the SN1 reaction depend on?

A
  • The carbon skeleton
  • The leaving group
  • Temperature
  • Solvent
    but NOT the nucleophile
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20
Q

Describe the contrasts between SN1 and SN2

A
  1. Steric hindrance - drives SN1 reactions as stabilises the carbocation + hinders approach of nucleophile
  2. Stereochemistry - SN1 reactions loose stereo control + obtain racemic mixture (if starting with a chiral centre) whereas SN2 reactions you invert the stereochemistry
  3. Solvent effects - SN1 performed in polar protic solvents whereas SN2 performed in aprotic less polar solvents
  4. Leaving group effect - play an important role in both SN1 and SN2 reactions and halides are driven by pKa and bond strength
  5. Nucleophiles - Sn1 reactions the nucleophile isn’t important whereas SN2 they are essential
  6. Amines - give multiple products
  7. Sulphur is better than oxygen - thiols are more acidic than water - easier to deprotonate
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21
Q

For alkenes what is reactivity controlled by?

A
  • How electron rich the double bond - it is a nucleophile
22
Q

Describe the double bond in alkenes

A
  • Slightly polar
  • pi bond is polarisable, so instantaneous dipole-dipole interactions occur
22
Q

Describe the conversion of alkenes (isomers)

A
  • Requires breaking of the pi bond between the two sp2 carbons
  • Alkene cis to trans conversion
23
Q

Describe how alkenes can be prepared.

A
  • Cracking - industrial process
  • Elimination reactions of halides/alcohols
24
Q

Describe the mechanism for alkenes.

A
  • Addition reactions via electrophilic addition
  • Electron movement from double bond to electrophilic centre
  • Addition reactions can either be: homolytic (involves radicals) or heterolytic (involves cations)
  • Nucleophile adds to the carbocation/radical
25
Q

Alkenes - Addition of H-X
What step is carbonation formation?

A

The rate limiting step

26
Q

Alkenes - Addition of H-X
What controls the outcome of reaction?

A

Carbocation stability (tertiary more stable than primary/secondary)

27
Q

Describe the anti-markovnikov addition (Alkenes)

A
  • In the presence of peroxides HBr adds to an alkene; through a radical mechanism
28
Q

Why is HBr only involved in the anti-markovnikov addition reaction?

A
  • ONLY HBr has the right bond energy
  • HCl bond is too strong, HI tends to break heterolytically to form ions.
29
Q

Describe the hydrogenation of alkenes to alkanes.

A
  • Syn or Cis addition
  • Reaction is stereospecific
  • Catalyst required (Pt, Pd or Ni)
30
Q

Describe Alkynes.

A
  • Unsaturated
  • Contains triple C-C bonds; comprised of a sigma bond and two weaker pi bonds
  • Reactivity dominated by reactive electron rich C-C triple bond
  • Triple bond acts as a nucleophile
  • Reactions similar to alkenes
31
Q

What is the general formula of alkynes?

A

CnH2n-2

32
Q

Describe the properties of alkynes.

A
  • Virtually insoluble in water
  • Stronger van der Waals forces
  • Internal alkynes higher boiling points than terminal
33
Q

Describe the reactivity of alkynes

A
  • Completely burns in O2
34
Q

State the reactions alkynes are involved in.

A
  • H-X addition
  • X-X addition (Br2, Cl2)
  • H-H addition (hydrogenation)
  • H-OH addition (hydration)
35
Q

State the general properties of haloalkanes.

A
  • Act as electrophiles
  • Reactivity controlled by electron poor carbon
36
Q

Describe the general properties of alcohols

A
  • oxygen is sp3 hybridised
  • Acts as nucleophiles
  • Reactivity controlled by electron rich oxygen
37
Q

Describe the physical properties of alcohols

A
  • As homologous series increases there is a similar increase in melting and boiling point
  • Unusually high boiling points due to hydrogen bonding between molecules
  • Small alcohols are miscible in water but solubility decreases as the size of the alkyl group increases
38
Q

Describe the inductive effect in alcohols.

A

Acidity decreases as alkyl group increases

39
Q

What is meant by electron withdrawal (alcohols)?

A

Halogens increase the acidity

40
Q

Describe the influence of hydrogen bonding in phenol.

A
  • Raises its melting point and boiling point
  • Increases solubility in water
  • Higher acidity than alcohol
  • Phenoxide stabilised by resonance
41
Q

Describe the biological importance of epinephrine (phenols).

A

The principle hormone governing the “fight or flight” response
- Also triggers a variety of physiological events, including increased heart rate

42
Q

Describe the structure and bonding of amines.

A
  • N is sp3 hybridised with the lone pair of elections in an sp3 orbital
  • tetrahedral geometry
  • High electrostatic potential at nitrogen; reactivity of nitrogen lone pair dominates properties of amines
43
Q

Describe the reactivity of amines.

A
  • The lone pair of electrons on nitrogen makes amines basic and nucleophilic
  • React with acids to form acid-base salts and they react with electrophiles
44
Q

Why are amine drugs given in salt form?

A
  • Amine salts are more soluble in water than the parent amines - they will readily dissolve in body fluids
45
Q

Describe the bonding in carbonyls.

A
  • Trigonal planar sp2 carbon and oxygen
  • All sigma bonds lie in the same plane; 120 degrees apart
  • C-O pi bond between parallel p orbitals on carbon and oxygen
46
Q

Describe carbonyl interactions at binding sites.

A
  • Planar, significant dipole moment
  • May interact with binding site through:
    Hydrogen bonding (carbonyl group is a hydrogen bond acceptor and two lone pairs on oxygen)
  • dipole-dipole interactions
47
Q

Describe reactions at the carbonyl carbon

A
  • Electron pair moves from C=O bond to electronegative oxygen atom producing tetrahedral alkoxide ion intermediate
  • Formation of new bonds increases steric crowding
  • Introduction of a chiral centre (carbonyl carbon sp2 -> sp3)
48
Q

State good nucleophiles for the reactions at the carbonyl carbon

A

Hydride
Alkynyl anion
Alkoxides

49
Q

How can the reactivity of carbonyl groups be enhanced?

A

By protonation of the carbonyl oxygen (to make the conjugate acid)

50
Q
A

Medicinal Chemistry (21 decks)

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