alkenes Flashcards

1
Q

Define electrophile

A

A species that accepts a lone pair of electrons.

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2
Q

What is a π bond? (with diagram

A

The sideways overlapping of p-orbitals.

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3
Q

Give 2 differences between σ and π bonds

A
  1. π bonds have a lower bond enthalpy than σ bonds.
  2. σ bonds have electron density between bonding atoms
    WHEREAS π bond have electron density above and below bonding atoms (so are more exposed/prone to attack).
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4
Q

What are stereoisomers?

A

Same structural formulae but different spatial arrangement of atoms.

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5
Q

What is required for E-Z stereoisomerism to arise?

A
  1. A double C=C bond (which provides limited rotation).
  2. Two different groups on each carbon atom around the double
    bond.
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6
Q

Describe the Cahn-Ingold- Prelog (CIP) priority rule

A

● Identify the priority groups on either side (the atom with the larger atomic mass).
● If the priorities are on the same (zame) side, it is a Z-isomer. If the priorities are on opposite sides (epposite), it is a E- isomer.
● If the directly attached atoms are the same, move onto the next atom

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7
Q

What is E/Z isomerism?

A

An example of stereoisomerism where…
● There is restricted rotation about the C=C.
● Two different groups attached to each C of the C=C group.

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8
Q

What is cis-trans isomerism?

A

A special case of E/Z isomerism (and thus stereoisomerism) where a substituent group on one C of the C=C group is the same as the other C

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9
Q

What is the hydration of alkenes and its conditions?

A
● Forming alcohols from alkenes. ● Conditions:
○ Steam.
○ Phosphoric acid catalyst.
○ Around 300°C
● Example:
○ C2H4 + H2O → C2H5OH
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10
Q

What is hydrogenation of alkenes and its conditions?

A

● C2H4 + H2 → C2H6.

● With hydrogen in the presence of a nickel catalyst at around 150°C.

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11
Q

Describe and draw the electrophilic addition between bromine and ethene

A

Br2 molecule approaches alkene.
2. Electrons in the π bond induce a temporary dipole the Br2
thus causing the Brδ+ to attack the electron dense π bond
whilst the Br-Br bond breaks by heterolytic fission.
3. The positive carbon on the carbocation intermediate attracts the Br- ion

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12
Q

Describe the electrophilic addition of hydrogen bromide and butene

A
  1. As the HBr (polar molecule) approaches the double bond, the Hδ+ attacks the electron dense π bond whilst the hydrogen- halogen bond breaks by heterolytic fission.
  2. This forms a carbocation intermediate which attracts the Br- atom
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13
Q

What is Markovnikov’s rule and what is used to do? (both with and without 1H)

A

● That the Hδ+ in the hydrogen halide will attach to the carbon with more hydrogens attached.
● It’s used to determine the major and minor products of electrophilic addition between hydrogen halides and asymmetric alkenes.
● For ICl, the Iδ+ will bond with the carbon with more hydrogens attached to it since it is less electronegative (just like Hδ+).

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14
Q

What conditions are required for polymerisation?

A

● High temperature. ● High pressure.
● A catalyst.
The specifics depend on the product you want to form.

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15
Q

What limits biodegradable plastics

A

Not having the right conditions to decompose (i.e., moisture and oxygen).

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16
Q

Give 3 ways of dealing with waste polymers

A
  1. Separating and recycling.
  2. Used as feedstock for cracking.
  3. Combusting for energy production.
17
Q

What are the problems of combusting polymers?

A

Can lead to toxic fumes (e.g., HCl).