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La Chimie H2 > Introduction à la chimie organique > Flashcards

Introduction à la chimie organique Flashcards

1
Q

What are the types of structural formulae?

A
  • Condensed structural formula
  • Displayed formula (full structural formula)
  • Skeletal formula
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2
Q

Organic compound can b classified into what 2 main grp in terms of their carbon skeleton? Describe both

A
  • Aliphatic/Alicyclic (non-aromatic)
    Aliphatic -> C atoms joined in open chains (straight or branched)
    Alicyclic -> C atoms joined in non-aromatic rings (alicyclic ring)
  • Aromatic
    contains benzene
    aromatic hydrocarbon
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3
Q

Organic compounds oso can b classified into what 2 main grp in terms of degree of saturation?

A
  • Saturated (oni single bond)
  • Unsaturated (hv multiple bonds eg double bond)
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4
Q

Define functional grp

A

an atom/grp of atoms common to series of organic compound that effectively determine principal chemical properties (eg type of rxn) of series

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5
Q

Define homologous series

A

series of compounds w same functional grp & general formula

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6
Q

What is an R- grp?

A

usually denotes alkyl grp, a grp derived fr alkane by removal of H atom -> general formula of R grp is -CnH 2n+1
eg methane -> methyl

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7
Q

What to take note of when naming organic compounds?

A
  • find parent chain FIRST
  • identify principal functional grp
  • use correct stem (eg meth-, eth-, etc.)
  • use di, tri, tetra, etc. if > 1 of same substituent
  • number & word separated by -
  • use lowest possible number
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8
Q

Define isomers

A

compounds that hv same molecular formula but diff structural formula

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9
Q

What are the 2 classes of isomerism? give eg for both

A
  1. constitutional (structural) isomerism
    eg
    - chain
    - positional
    - functional grp
  2. stereoisomerism (same formula, structural formula but diff in 3D space)
    eg
    - cis-trans
    - enantiomerism
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10
Q

Define chain isomer

A

constitutional isomers w diff arrangement of C chain

eg butane vs 2-methyl propane

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11
Q

Define positional isomer

A

constitutional isomers w diff pos n of same functional grp on C chain/ring

eg 1-chloropropane vs 2-chloropropane
OR
propan-1-ol vs propan-2-ol

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12
Q

Define functional grp isomer

A

constitutional isomers w diff functional grp present

eg ethanoic acid vs methyl methanoate

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13
Q

What are criteria for cis-trans isomerism?

A

A compound will exhibit cis-trans isomerism if:
1. there is restricted rotat n abt a C=C bond due to presence of π bonds
2. there are 2 diff substituent attached to each C atom of C=C bond w restricted rotat n

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14
Q

What is the diff btw cis- & trans- isomer?

A
  • cis-isomer hv 2 identical grp on same side of C=C bond
  • trans-isomer hv 2 identical grp on opposite side of C=C bond
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15
Q

Why can we not use condensed formula eg -C3H7 but write as -CH2CH2CH3?

A

To avoid ambiguity

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16
Q

Which kind of alkene generally do not exhibit cis-trans isomerism? Why?

A

cyclic alkenes, oni hv cis configurat n

bcos to hv trans config, ring need b distorted (puckered), result in considerable ring strain, lead to instability

17
Q

What is the formula to predict no of cis-trans isomers?

A

max no of cis-trans isomers = 2^m

where m>0, m is no of C=C bonds that can exhibit cis-trans isomerism

18
Q

What are possible explanations to the reason:
- cis-isomer hv higher bp than trans-isomer?
- trans-isomer hv higher mp than cis-isomer?

A

(all bcos of shape; trans is zig-zag, cis is u shaped)

  • cis-isomer hv higher bp than trans-isomer
    more energy need to overcome stronger pd-pd attract n btw polar cis-isomer molecules than weaker id-id attract n btw non-polar trans-isomer molecules
  • (oni applicable if trans-isomer really hv higher mp than cis-isomer; otherwise similar expl n as above)
    trans-isomer hv more symmetrical, linear shape, enable closer packing of molecules in solid state. Thus, more extensive imf of attract n formed, require more energy to overcome
19
Q

Define chiral carbon. How to identify them in cyclic compounds?

A

a C atom w 4 diff atoms,grp of atoms bonded to it.

  • in cyclic compounds, found at 3/4 pt junctions, where both sides of ring from the junction are not identical
20
Q

What is in a stereochemical formula (showing 3D spatial arrangement of atoms in molecule and molecule shape)?

A
  1. ____(bonds on same plane as paper)
  2. ||||||(bonds behind plane of paper; away from you)
  3. solid wedge/solid long triangle (bonds out of plane of paper; towards you)
21
Q

What are the criteria for enantiomerism?

A

a molecule exhibits enantiomerism/ exists as enantiomers if it hv:

  • non-superimposable (not same exact molecule) mirror image
  • 1 or more chiral C atom
  • no plane of symmetry
22
Q

What are properties of enantiomers?

A
  • each enantiomer is optically active (can rotate plane-polarised light)
  • hv identical chemical properties (except in interact n w another chiral molecule)
  • hv identical physical properties EXCEPT in direct n in which they rotate plane-polarised light
  • enantiomers rotate light oppositely; (+) enantiomer rotate plane-polarised light clockwise, (-) enantiomer rotate plane-polarised light anti-clockwise
23
Q

Define racemic mixture. What is one property of such mixture? Why?

A
  • a mixture containing equal amt of each enantiomer
  • mixture is optically inactive since no NET rotat n of plane polarised light

bcos both (+), (-) enantiomers rotate plane polarised light thru equal angle but in opp direct n. Hence, rotat n caused by 1 enantiomer is exactly cancelled by rotat n caused by other enantiomer

24
Q

What is the formula to predict no of enantiomers?

A

max no = 2^n

where n>0, n is no. of chiral C in molecule

25
Q

What is the formula to determine TOTAL no of stereoisomers (cis-trans & enantiomers)

A

max no. = 2^(m+n)

where m, n >0,
m is no of C=C bonds that can exhibit cis-trans isomerism,
n is no of chiral C in molecule

26
Q

What are biological properties of enantiomers? Explain

A
  • diff stereoisomers exhibit diff biological properties eg in drug action
  • most drugs r chiral. Typically, oni 1 of stereoisomers (eg oni 1 of 2 enantiomers) of drug provides desired biological effect. The other mirror image form can b less active & toxic
    => bcos to exert biological action, chiral drug molecule must fit into chiral receptor at some target site in body. Oni 1 of mirror images can fit properly into receptor to exert biological action. The other mirror image is thus inactive or may interact w other unintended receptors, giving rise to undesired side effects
27
Q

What type of hybridisation in C atom is present if there are:
- 4 σ bonds?
- 3 σ bonds?
- 2 σ bonds?

A
  • 4 σ bonds - sp3 hybridised
  • 3 σ bonds - sp2 hybridised
  • 2 σ bonds - sp hybridised

(Tip: remember no of σ bonds then minus 1 to get sp…
eg 4 σ bond –> 4-1=3 –> sp3 hybridised)

28
Q

Explain the formation of following hybrid orbitals, along with shape, bond angle around C:
i. sp3
ii. sp2
iii. sp

A

i. sp3
- 1 s, 3 p orbitals (s,px,py,pz) r involved in hybridisat n process
- 4 sp3 hybrid orbitals r formed
- tetrahedral, 109.5°

ii. sp2
- 1 s, 2 p orbitals r involved in hybridisat n process
- 3rd p orbitals remain unhybridised
- 3 sp2 hybrid orbitals r formed
- trigonal planar, 120°

iii. sp
- 1 s, 1 p orbitals r involved in hybridisat n process
- 2 other p orbitals remain unhybridised
- 2 sp hybrid orbitals r formed
- linear, 180°

La Chimie H2 (25 decks)

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