R3.4 Electron-pair sharing electrons (PART 2)

Bronsted-Lowry Theory Recap

• Acid - proton DONOR

  • loses hydrogen

• Base - proton ACCEPTOR

  • gains hydrogen

Lewis acid base theory - defines acids/bases in terms of electron pair transfer

• Lewis acid - electron pair ACCEPTOR

  • gains electrons

• Lewis base - electron pair DONOR

  • loses electrons

• applies to both organic + inorganic reactions

  • Inorganic

    • metal cations are lewis acids

    • 

  • organic

    • electrophiles (lewis acid) - gains electrons

      • electrophile - electron deficient + attracted to electron rich

        • H⁺

        • Br⁺

        • NO₂⁺

    • nucleophiles (lewis base) - loses electrons

      • nucleophile - electron rich + attracted to electron deficient

        • H₂O

        • OH^-

        • NH₃

        • X^-

        • CN^-

      • 

Lewis theory is broader than bronsted lowry theory

• can be applied to wider range of chem reactions

All BL acids are Lewis Acids

• BUT not all lewis acids are BL acids

all BL bases are lewis bases

• BUT not all lewis bases are BL bases

lewis acid reacts w lewis base → coordinate covalent bond

complex ions

• transition metal + ligand

• formed through lewis acid-base reactions

• Coordination # - number of coordinate covalent bonds on central metal ion

• charge - overall charge of complex ion

  • sum of cation + ligand charges

Alkenes - double bonded molecules

• unsaturated - double bond

  • double bond = nucleophile

    • high electron density

    • attracted to electrophiles

  • sigma bond - the first bond formed btwn 2 atoms

  • pi bond - the double/triple bonds but not the sigma bond

Polymers - large molecules (macromolecules) made from monomers

• monomers - repeating subunits

• classified into 2 main categories

  • natural - found in nature

    • sugars, proteins, DNA, silk, cellulose

    • play crucial role in biological processes

  • synthetic - human made

    • plastics, clothing

    • created through polymerization

      • addition polymers → plasics

      • condensation polymers → clothing

    • properties of plastics

      • flexible

      • durable

      • moldable

      • lightweight

      • electrical/thermal insulators

• physical properties of polymers

  • determined by nature of monomer + way they are linked together

    • intermolecular forces

Addition polymerization - breaking a double bond in each monomer to create new bonds linking the monomer units together

• monomer must be an alkene

• pi bond broken in each monomer → single bond forms btwn monomers

• represent the repeating unit of an addition polymer when given the monomer structure

  • structural formula of a specific number of repeating units

  • OR repeating units in brackets with subscript of n

• deduce monomer for addition polymers when given polymer structure

  • monomer is ALWAYS an alkene

naming polymers

• determine polymer structure (alkene)

• name the monomer via IUPAC

• put poly in front

electrophilic addition to alkenes

• double bond in alkene breaks

• 2 additional atoms bond with the molecule

  • 1 atom bonds to each carbon in the double bond

• product = saturated compound

types of electrophilic addition to alkenes

• halogenation - addition of halogens (X2)

  • forms di-halogenoalkane

• hydrohalogenation - addition of HX

  • forms halogenoalkane

• hydration - addition of water

  • forms an alcohol

symmetrical alkenes

• identical substituent groups attached to carbons

  • double bond = line of symmetry

• mechanisms are drawn

asymmetrical alkenes

• different substituent groups attached to carbons

  • no line of symmetry

• products are predicted

Halogenation: alkene + H2

• Step 1

  • double bond e- induces dipole on X2 + attack electrophilic end

    • electrophilic end = partially positive end

  • forms carbocation intermediate + negative halide ion

• Step 2

  • halide ion attacks carbocation

• If 2 different halogens (ex. ClF) → less electronegative halogen binds to carbon w most hydrogen

hydrohalogenation: alkene + HX

• Step 1

  • double bond e- attacks H

    • polar bond where H is partially positive

  • forms carbocation intermediate + negative halide ion

• Step 2

  • halide ion attacks carbocation

hydration: alkene + H2O (water)

• Step 1

  • double bond e- attacks H

    • polar bond where H is partially positive

  • forms carbocation intermediate + hydroxide ion

• Step 2

  • hydroxide attacks carbocation

Unsymmetrical alkenes

• unsymmetrical alkenes react with HX OR H2O → 2 products can form

• how to determine major product

  • stability of carbocation intermediate

    • more stable carbocation intermediate is favored → most stable is major product

major product can be predicted using Markovnikov’s Rule

• Markovnikov’s rule - hydrogen atom will attach to the carbon w more hydrogens

Benzene C6H6 - most common aromatic compound

• cyclic

• planar

• 3 double bonds in resonance

  • high electron density

  • acts as nucleophile

    • attracted to electrophiles

• extremely stable

  • delocalized electrons = resonance = stability

  • double bonds do not want to break

• Favors substitution over addition reactions

electrophilic substitution

• high activaction energy for reaction

• unstable carbocation intermediate

• final product is stable

  • aromaticity + resonance is re-established when H is lost

electrophilic aromatic substitution mechanism

• Step 1

  • E+ added to ring → loss of aromaticity

• Step 2

  • removal of H → reconstitutes aromatic ring

condensation polymer - polymer formed by reaction btwn 2 functional groups with the release of a small molecule

• small molecule is usually water

• categorized according to the functional group present on repeating unit

IB requires to draw the repeating unit of polyesters/polyamides when given the monomer structures

• polyesters and polyamides are formed form the combo of 2 different monomers

polyesters - most commonly used in fabrics/fibers

• Ester functional group produced from alcohol + carboxylic acid

• be mindful which atoms are lost to form the water molecules

  • H - from alcohol

    • single bonded O ends the alcohol side

  • OH - from carboxylic acid

    • C=O at the carboxylic acid end

polyesters formed from combos of monomers that each have 2 functional groups

• diol (2 hydroxyls) + dioic acid (2 carboxyls)

polyamides - used in ropes, seatbelts, and dental floss (most common = nylon)

• amide functional group produced from amine + carboxylic acid

• be mindful of which atoms are lost to form the water molecules

  • H - from amine

    • single bonded -NH ends the amine side

  • OH - from carboxylic acid

    • C=O at the carboxylic end

polyamides produced from combos of monomers that each have 2 functional groups

• diamine (2 aminos) + dioic acids (2 carboxyls)