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OCR A-level Chemistry Module 4: Core Organics > Alkenes > Flashcards

Alkenes Flashcards

WHOLE lot more to learn, so treat it royal :D

1
Q

What are alkenes?

A
  • Unsaturated hydrocarbonds!
  • Can be Branched, Cyclic and Linear!
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2
Q

What is a π - bond?

A
  • Where 2 P-Orbitals sideways overlap, with e- density ABOVE AND BELOW line joining BOTH C atoms
  • Always occurs where C=C takes place!
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3
Q

Difference with σ-bond and π-bond?

A
  • Pi = 2 regions of e- density ABOVE AND BELOW line - weaker than sigma bond, 2 p orbitals overlaping
    Sigma = everything of opposite!
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4
Q

How can we describe the C=C bond in detail?

A
  • Bonding around carbon with 3 sigma, 1 pi bond (always!!!) = 3 REGIONS OF e- DENSITY!
  • 3 bonding regions, 0 lone pairs = 120’
  • pi bond locks 2 carbons in position, preventing ROTATION AROUND C=C BOND!
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5
Q

What gives C=C bond its strict rigidity?

A
  • Due to pi-bonds e- density position ABOVE AND BELOW plane of sigma-bond!
  • will mean that groups attached per carbon will be fixed, relative to each other!
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6
Q

What is Stereoisomersim?

A

Where same structural formula, different arrangement in space!

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7
Q

What is E/Z Isomerism?

A
  1. This is when different groups attached to each carbon in C=C has different arrangement in space, restricted due to no rotations!

italics = both conditions needed to be met!

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8
Q

What makes an E and Z isomer?

A
  1. E = group in common will be on opposite sides of molecule, mirroring position in space!
  2. Z = group in common will be on the same side of molecule in space!

ZAME side on the SAME side!

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9
Q

Difference with Cis-Trans and E/Z Isomerism

A
  1. CIS-TRANS = Special case of E/Z isomerism, where carbons in C=C must still have differing groups, but 1 OF THE GROUPS MUST BE THE SAME IN BOTH CARBONS!
  2. TRANS = same group attached to C=C on opposite side of molecule! = TRANS = E
    Hence, ALL cis-trans are a type of E/Z, but not vice versa
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10
Q

What is Cahn-Ingold-Prelog nomenclature?

A
  1. Atoms attached per carbon atom in C=C are given PRIORITY BASED ON ATOMIC NUMBER
  2. Groups of higher priority on same side = Z isomer
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11
Q

What to do with Cahn-Ingold-Prelog when with complex groups?

A
  • we have to observe the FIRST POINT OF DIFFERENCE on the complex groups!
  • if this point has higher atomic number, higher priority is then assigned!
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12
Q

Why are alkenes more reactive than alkanes?

A
  1. Due to pi-bond precense, meaning high e- density outside of C=C
  2. Greater exposure, with weaker pi-bonds = less energy required to break, and donate electrons…
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13
Q

How does Hydrogenation and Halogenation work?

A
  • HYDRO: Hydrogen gas + nickel catalyst, at very high tempratures (removing double bond&raquo_space; alkane)
  • HALO: Halogen gas reacted under room temprature, rapidly, (removing double bond via ADDITION&raquo_space; alkane)
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14
Q

How does Hydration and Bromine Test work?

A
  1. HYDRATE: Alkene + H2O under phosphoric acid catalyst presence, gives extra H and OH group = ALCOHOL!
  2. BT: Identifying presence of C=C bond, being unsaturated, Orange-Brown>Colourless
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15
Q

Mechanism for Electrophilic Addition?

A
  1. Halogen Halide/Halogen as polar/iunduced molecule has gained e- pair from alkene C=C, while undergoing heterolctic fission
  2. Carbocation formed, anion gained e- pair, and bonds to carbocation
  3. New molecule formed! (all shown via CURLY ARROWS!!!!!!)
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16
Q

What is Markownikoff’s Rule?

A
  1. This describes when a halogen halide reacts with an asymmetrical alkene, the hydrogen atom will attach itself to the carbon atom with the most hydrogen atoms!

TO REMEMBER: “The rich get richer”, carbon with most H = richest!

17
Q

Describe carbocation stability!

A
  1. The more hydrogen atoms present on C, the LOWER THE STABILITY
  2. LOWER STABILITY = GREATER CHANCE FOR HALIDE TO ATTACH TO C OF CARBOCATION (+)
  3. Hence, primary>secondary>tertaity carbocation is order!
  4. Order due to more alkyl groups present, the greater the spread of positive charge via carbocation, meaning greater stability
18
Q

How to draw 2,3,4 ect repeating monomers?

A
  1. Draw the monomers joined together, with a line continuing from both ends (n not even needed)
19
Q

Environmental concerns for POLYMERSSSSS WASTE!

A
  1. Incinerating for energy source (but PVC will release HCL into air if burnt = toxic)
  2. Feedstock recyclying, suitable for unsorted + unwashed polymers, products used as raw material in manufacure of new polymers
  3. Biodegradeable/photodegradeable polymers, natural breakdownvia microorganisms!

OCR A-level Chemistry Module 4: Core Organics (4 decks)

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