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PChem > Functional Groups > Flashcards

Functional Groups Flashcards

1
Q

Functional Groups

A
  • A potentially reactive unit within a molecule
  • Drugs typically are multi-functional molecule
  • Sometimes FG are the basic framework of the molecule (Core or scaffold) or they a are appendages to the structures (substituents)
  • They work together as a team, cannot be dissected
  • E- are shared throughout the FG
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2
Q

FG within Drug Molecules affect:

A
  • How a drug is transported
  • How it binds to its receptor
  • How it causes a biological response
  • How it undergoes metabolism
  • How it gets excreted from the body
  • The drug stability during storage
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3
Q

FG (common carbonyl containing)

A

Ketone, Aldehyde, Carboxylic Acid, Ester, Carbonate, Amide, Carbamate, Urea, Lactone(cyclic ester), Lactam (cyclic amide)

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4
Q

FG (common nitrogen containing)

A
  • Amine (basic, 1,2,3)
  • Ammonium (can be acidic)
  • Quaternary ammonium (permanent (+) charge
    – Doesn’t give or accept protons
  • Nitro,
  • Nitrile
  • Imine (basic)
  • Amidine (p-orbital)
  • Guanidine(strongest basic FG in amine)
  • Imide
  • N-Acylsulfonamide
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5
Q

FG (common sulfur containing)

A
  • Thiol (Mercaptan)
  • Sulfide (Thioether)
  • Sulfoxide
  • Sulfone
  • Sulfuric Acid
  • Sulfonate
  • Sulfate
  • Sulfonamide
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6
Q

FG (Miscellaneous FG)

A
  • Alcohol
  • Phenol
  • Enol (the En means a double bond)
  • Ether
  • Fluoro
  • Chloro
  • Bromo
  • Lodo
  • Trifluoromethyl
  • Phenyl
  • Benzyl
  • Alkyl
  • Alkenyl
  • Alkynyl
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7
Q

Tautomerization

A
  • Some FG are capable of existing in two forms
  • Break bond and form another
    Ketone (favored) can turn into Enol (hydrogen migrate to carbonyl oxygen to form a O-H bond
  • So tautomers are two structure that only differ with respect to the point of attachment of the H and the location of double bond
  • The equilibrium depend on stabilities (Keto is favored compared to Enol)
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8
Q

Imine - Enamine

A
  • Imine form is strongly favored - Examines are generally stable only if they lack hydrogen on N
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9
Q

Oxime - Nitroso

A

Favor oxide form

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10
Q

Electronic Effects

A
  • Single bonds formed between atoms of different electronegative will be polarized
    – In such bonds e- will be attracted by the more electronegative atom which will induce a small amount of (+) charge
    – This will attract e- in the adjacent bond that will induce a smaller amount of (+)
  • This is called inductive effect and it decrease with distance
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11
Q

Field effect

A
  • When polarization happen through space rather than through bonds
    – Two groups of different elctronegativities need only to be close to one another for the field effect to be observed
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12
Q

Polar Effect

A

The two field effect and inductive effect together are to as Polar Effect
- As it is difficult to differentiate
- It decrease with distance from the more electronegative element

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13
Q

Resonance

A

Conduction of electrons throgh a conjugated system
- More favorable (lower in E) to disperse electron density over several atoms rather than have it concentrated at one point
- Resonance does not decrease (significantly) with distance

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14
Q

Conjugated System

A

There is alternating single and double bonds

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15
Q

Electron-Donating Groups

A

Transfer (donate) electrons density into a molecule as needed
- In response to a developing positive charge (usually)

EDG Function Groups
- Alcohols, ethers, amine, thiols, thioethers (sulfides), alkyl groups, and aromatic rings (can be e- withdrawing)

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16
Q

Alcohol and Ether

EDG

A

Delocalize the lone pair on O to develop area of + charge
- An example of resonance, and help to lower the energy of compound
- It spread out the charge over several atoms => lower the energy relative to having the charge centered on a single atom

17
Q

Thiols and Thioethers (sulfides)

EDG

A

Work in the same way as their Oxygen analogs
- Sulfur is much larger than carbon => p-orbital overlap to form C=S is less efficient than C=O bond
- This mean that they are less efficient as EDG compared to alcohols and ethers

18
Q

Amines

EDG

A

Same mechanism as alcohols but with N
- It’s less electronegative than O so it can tolerate positive charge better
- Amines are an excellent electron donators (better than sulfure and oxygen containing groups)

19
Q

Alkyl Groups

A

Include substituents as methyl, ethyl, propyl, etc.
- Capable of dislocalizing adjacent positive charge by a process called hyperconjugation
– As there are no lone pairs to delocalize, the e- in adjacent C-H bonds are instead used for the same purpose
— While it cost energy to break the C-H bond, it is compensated for by dispersing the change through resonance
—- The greater the number of adjacent hydrogens, the better the EG properties (more resonance structures)
—– Methyl>Ethyl>i-propyl>t-butyl

20
Q

Aromatic Rings

EDG

A

Use pi-electron density to help stabilize the adjacent charges by delocalizing that charge (olefins and alkynes do the same)
- Ex. In a Benzene (+) charge can be delocalized onto both oortho-prosition and para position

21
Q

Electron-Withdrawing Groups

EWG

A

Withdraw e- density from a system; act as sink point for excess e- density
- They stabilize existing or developing (-) charge at or near point of attachment
- Many possess double or triple bonds
– All carbonyl based functional groups, cyano, nitro, sulfonyl, sulfinyl
- Imino-type functional groups
- Halides withdaw as do aromatic rings, olefins, and alkynes

22
Q

Carbonyls

EWG

A

Withdraw e- density by two mechanisms
- Inductive effect
– The electronegativity difference between carbon and oxygen polarizes the bond; O will have partial negative and C will have partial positive (decrease with distance)
- Resonance
– e- density can be delocalized by resonance through the C=O bond which can spread the charge over several atoms
— Delocalize negative charge

23
Q

Carbonyls with esters and amides

A

They are heteroatoms; a lone pair can be pushed into carbonyl group by resonance
- Reduces the degree of + charge that builds on the C of the carbonyl group
– This means that relative to ketones and aldehydes, esters and amide are slightly WEAKER EWG
— This mean when we end up with both a - and + sign on the structure after resonance=> weaker EWG

Only EWG when attached to substrate at carbonyl carbon
- Acetyle oxy
- Acetomide group

If position of attachment is heteroatom (any atoms that is not C or H) then it behave as weak ED substituents

24
Q

Nitriles

EWG

A

Have a C-N triple bond
- More electronegative than C => the bond is polarized (Charge only go in one direction-toward N)
- Resonance is important to disperse excess electron density

25
Q

Nitro Groups

EWG

A

(-NO2) are among the strongest EWG
- The N always carries a + charge (4 bonds) and one O has a - charge

26
Q

Sulfoxides

A

Sulfure forms four bonds
- Two to neighboring groups
- A double bond to O

Sulfur larger than Oxygen
- pi-bond formation is less efficient than C=O
- This means that a significant resonance form must exist with a
– (+) charge on S (to stabilize the - charge)
– A Single bonded O having a (-) charge

Aceyl (C=O) is more e- withdrawing

27
Q

Sulfones (sulfonyl)

A

Sulfur form 6 bonds
- Two to neighboring groups
- Two double bonds to O

As with sulfoxides (S=O) a significant resonance form exist with
- (+) charge on S
- (-) charge on a single bonded O (one of the two)

As there are two O; this mean there is an additional resonance structure = stronger e- withdrawer
- Sulfones > Acyl > Sulfoxides

28
Q

Halides: Fluorine

EWG

A

Despite it’s very high electronegativity; a single F is only weakly EW
- it’s strong withdrawing effect is offseted by back donation (resonace) into vacant antiboding orbital

F>Cl>Br>I

29
Q

Halides: Cl, Br, I

EWG

A

The size difference between them and C makes back donation by resonance inefficient
- They withdraw mainly by polar effect (Cl and Br)
– F > Cl > Br > I

30
Q

Trifluoromethyl

EWG

A

CF3 is a powerful electron withdrawing
- The three F attached to one C allow the polar effect of each one to attract e- density from the other
– Prevent their lone pair from being back-donated

31
Q

Aromatic Rings

A
  • The pi-system can respond to both (+ and -) charges on adjacent carbons
    – the presence of other EWG makes aromatic rings even stronger electron withdrawing group => charge is spread over more atoms
31
Q

Aromatic Rings

A
  • The pi-system can respond to both (+ and -) charges on adjacent carbons
    – the presence of other EWG makes aromatic rings even stronger electron withdrawing group => charge is spread over more atoms

PChem (6 decks)

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