organic materials Flashcards
amino acid ‘R-group’ properties
(side chain)
polar (OH) / non-polar (CH₃)
proton donor (COOH) / proton acceptor (NH₂)
acid-base properties of amino acids
di-functional from NH₂ & COOH
∴ amphoteric depending on pH of the solution environment
NH₂ → NH₃⁺ & COOH → COO⁻
zwitterion in solution
(dipolar ion)
overall neutral amino acid containing both positive & negative change
present at isoelectric point (pH)
amino acid in low pH (pH < pI)
zwitterion + abundance of H₃O⁺ → cation + H₂O
amino acid in high pH (pH > pI)
zwitterion + abundance of OH¯ → anion + H₂O
condensation polymerization reaction of 2-amino acids (α-amino acids)
NH₂ & COOH react together to form a peptide (amide) link (CONH) + H₂O
N-terminal amino acid
end of the polypeptide chain with a free amino group
C-terminal amino acid
end of the polypeptide chain with a free carboxyl group
primary structure of protein
sequence of amino acids joined by covalent peptide bonds
secondary structure of protein
hydrogen bonding between N-H & C=O causes folding into α-helices (polypeptide coils into a spiral) or β-pleated sheets (polypeptide folds into parallel layers)
tertiary structure of protein
3D shape formed through forces between R-groups of amino acids
e.g. covalent disulfide bridge (S-S) & ionic salt bridge (NH₃⁺/COO⁻)
(hydrogen bonding, dipole-dipole attraction, dispersion forces)
interial hydrophobic & exterial hydrophilic R-groups
quarternary structure of protein
multiple polypeptide chains (& sometimes non-protein molecules) form large complex functional units held together by dispersion forces
(e.g. haemoglobin)
hydrogen bonding, dipole-dipole attraction & ionic interactions may also be present
characteristics of biological enzymes
proteins that catalyze biochemical reactions by providing an alternate reaction pathway with lower activation energy
sensitive as changes in temperature or pH may disrupt the forces that determine their tertiary structure
active sites are substrate specific
describe the effect of changing temperature/pH on an enzyme ?
enzymes are are temperature/pH specific
changes can disrupt the forces that determine their tertiary structure
active sites no longer binds to the substrate
triglycerides
condensation reaction between glycerol (propane-1,2,3-triol) & 3 fatty acids
OH (glycerol) + COOH (fatty acid) → ester link (COO) + H₂O
saturated fatty acids
hydrocarbon chains with only C-C bonds
unsaturated fatty acids
monosaturated : hydrocarbon chains with one C=C bond
polysaturated : hydrocarbon chains with multiple C=C bonds
omega & alpha carbons
omega : last carbon furthest away from COOH
alpha : first carbon within COOH
melting point of triglycerides
↑chain length = ↑melting point
∵ ↑dispersion forces
↑C=C bonds = ↓melting point
∵ cis-arrangement bends the hydrocarbon chain
∴ ↓dispersion forces (fatty acids cannot pack tightly)
saponification (hydrolysis)
triglyceride + 3NaOH → glycerol + 3 fatty acid-COO⁻Na⁺ (soap)
soap as a medium between water & oil
charged COO⁻Na⁺ (hydrophilic) forms ion-dipole bonding with H₂O
non-polar hydrocarbon tail (hydrophobic) forms weak dispersion forces with oil
soap in water
soap clumps together to form a spherical micelle
hydrophilic ends (charged carboxylate group) face outwards & hydrophobic ends (non-polar hydrocarbon tail) face inwards
cleaning action of soap
agitation (washing) breaks the micelle & non-polar ends attach to the oil
ion-dipole bonding with water lifts the oil particles & non-polar ends surround the oil molecules to trap them (forming a micelle again)
soap in hard water
hard water contains metal ions (e.g. Mg²⁺, Ca²⁺) which react with soap (sodium stearate)
this creates magnesium/calcium stearates, which are insoluble in water
∴ poorly washed clothes & soap scum
glucose in solution
α-glucose (cyclic) : OH group on C₁ points down
β-glucose (cyclic) : OH group on C₁ points up
aldose vs ketose
glucose : aldose (terminal C=O)
fructose : ketose (non-terminal C=O)
disaccharides
condensation reaction between two monosaccharides’ OH groups (C₁ - C₄)
glycosidic bond (C₁-O-H + H-O-C₄ → C₁-O-C₄ + H₂O)
e. g. glucose + glucose → maltose + H₂O
e. g. glucose + fructose → sucrose + H₂O
e. g. glucose + galactose → lactose + H₂O
(C₁ loses H & C₄ loses OH)
starch (amylose)
linear glucose polymer with α-1,4-glycosidic bonds
starch (amylopectin)
branched glucose polymer with α-1,4-glycosidic bonds & α-1,6-glycosidic bonds
cellulose
linear glucose polymer with β-1,4-glycosidic bonds
amorphous regions
tangled arrangement of polymer chains
∴ weaker intermolecular forces
crystalline regions
ordered arrangement of polymer chains
∴ stronger intermolecular forces
low-density polyethene
created under high pressure & temperature; contains many disordered branches
∴ amorphous
∵ molecules cannot pack tightly (weak dispersion forces)
(low melting point, low density, soft)
high-density polyethene
created under low pressure & a transition metal catalyst; contains few ordered branches
∴ crystalline
∵ molecules pack tightly (strong dispersion forces)
(high melting point, high density, hard)
isotactic polypropene
regularly arranged methyl side groups all on one side of the polymer chain
∴ semi-crystalline
atactic polypropene
randomly arranged methyl side groups on either side of the polymer chain
∴ amorphous
syndiotactic polypropene
regularly arranged methyl side groups on alternating sides of the polymer chain
∴ crystalline
polytetrafluoroethene
↑melting point from strong C-C & C-F bonds
non-polar from symmetrical nature (although dipoles are present)
chemically inert from fluorine atom coating
(insoluble & non-stick)
polyester
condensation reaction between a di-ol & di-oic acid
ester link + H₂O
(e.g. PET)
co-polymer
advantages & disadvantages of polymers
advantages : mechanical strength; low density; generally chemically resistant
disadvantages : derived from non-renewables; not biodegradable; toxic when burnt
