chem unit 4 aos 1

organic compounds

carbon containing compounds that formed by linking C together to make life possible

allotropes def

the diff physical forms an element can exist in

why such a large diversity of organic compounds (why C can form so many compounds)

• electron arrangement of 4 valence electrons → can form 4 strong covalent bonds

• bonding can occur with diff element combos and in diff shapes

bond energy def

amount of energy needed to break bonds of a mole of molecules into individual atoms (intramolecular separation?)

• kj mol^-1

• indicates strength of covalent bond

bond energy depends on…

• atoms involved in sharing covalent bond

• distance between 2 atoms (bond length = distance between nuclei of the atoms sharing electrons) — shorter bonds usually more difficult to break

where is the evidence that carbon bonds are strong

the bond enthalpy table in databook showing large values

carbon bond angles

• four single covalent bonds = tetrahedral distribution, carbon is saturated

• double bond present (hence 2 remaining single bonds) = planar triangular distribution, unsaturated carbon (as one of the bonds in double bond weak → evidenced by bond enthalpy values in db)

• triple bond (hence 1 remaining single bond) = linear distribution, unsaturated (2 of the bonds in triple bond weak)

how is shape of molecule determined

by max repulsion of electron pairs in molec (hence into diff distributions like tetrahedral, planar triangular, linear etc)

carbon bonds relative strength

between 2 C atoms:

triple bond > double bond > single bond

in terms of being shorter and stronger

how can degree of unsaturation be measured

reacting compound with iodine

• the iodine number = mass of iodine that reacts with 100 g of the comp

• higher the number → the more iodine is reacted → the more unsaturated the comp is (the more double bonds there are? 1 mol of iodine reacts with 1 double bond?)

representing organic compounds

• molecular formula

• electron dot diagram (lewis struc)

• structural formula

• semi-struc (condensed) formula

• skeletal formula

representing organic compounds — notes

• semi-struc formula = written single line, each C atom followed by atoms joined to it, repeated CH2 gaps in brackets with subscript

• skeletal = at each end of line (vertex) there is C atom (with enough H atoms bonded to it to satisfy C’s valency) — any other atoms or bonds apart from C — H shown on diagram normally

homologous series def

org compounds with:

• similar strucs

• similar chem properties

• pattern to physical properties

• same gen formula

— consecutive members of same homologous series differ by CH2

hydrocarbons def

simplest org compounds made only of C and H

— mainly gotten from crude oil

aliphatic vs aromatic compounds

• aliphatic = org compounds where C atoms form open chains (alkanes, alkenes, alkynes)

• aromatic = has one or more benzene rings, alternating single and double bonds within ring

alkanes

• saturated hydrocarbons with only single covalent C — C or C — H bonds

• gen formula = C_nH_2n+2

saturated def

all bonds strong covalent bonds + no multiple bonds between C atoms for one to be weaker hence allowing breakage (and addition of other atoms into molec)

alkenes

• unsaturated hydrocarbons with at least 1 double bond between C atoms

• gen formula = C_nH_2n

— (think as 2 hydrogen atoms removed from alkanes hence double bond must form — gen formula makes sense)

alkynes

• unsaturated hydrocarbons with at least 1 triple bond between C atoms

• gen formula = C_nH_2n-2

— not in sd?

cyclic hydrocarbons

• ring strucs where C chain is closed struc w/o open ends

• gen formula = C_nH_2n ( same as alkenes !! - bc all C atoms covalently bonded to 2 others on either side)

• diff molecular formula to straight-chain alkanes

• prefix = cyclo- (e.g. cyclohexane)

• arenes are a grp of this

benzene

• produces arenes (aromatic, benzene-based hydrocarbons)

• molec with 6 electrons from 3 double bonds shared by all the carbons in the ring — attraction of electrons to all C atoms gives molec stability

alkyl groups

• hydrocarbon branches coming off longest C chain of org molecule

• suffix = -yl

• think as - if alkane has 1 or more H atoms removed (alkyl with same prefix as an alkane — the alkyl has 1 less H atom)

• R

IUPAC naming org compounds

1. selection of main C chain

2. numbering of main C chain

3. naming (prefix + stem + suffix)

— see notes for more detail

functional grp def

atom/atoms attached to hydrocarbon chain that influences molec chem and physical properties

molec with functioning grp attached usually…

less stable than C backbone hence more likely participate chem reactions

homologous grp with functional grps — haloalkanes

• one or more halogens attached to C chain

• R — X (R = alkyl group/the hydroc chain, X = halogen)

• prefix is halogen name with ‘ine’ ending replaced with ‘o’

• C_nH_2n+1X

homologous grp with functional grps — amines

• org compounds have amino functional grp

• R — NH2

• ‘-amine’ suffix replaces ‘ane’ (but note that stem will still have ‘an’ attached like pentan-1-amine)

• C_nH_2n+3N

homologous grp with functional grps — amides

• org compounds with amide functional grp (-CONH-) where N attached to carbonyl C

• R — CONH2

• smallest primary amide has functional grp = -CONH₂

homologous grp with functional grps — alcohols

• org compounds with hydroxyl (-OH) functional grp

• R — OH

• C_nH_2n+2O

• primary alcohol (C-OH the alkyl C attached to one other C), secondary alcohol (C-OH the alkyl C attached to 2 other C), tertiary alcohol (C-OH the alkyl C attached to 3 other C)

carbonyl grp

when C double bonded to O

homologous grp with functional grps containing carbonyl grp — aldehydes

• org compounds with aldehyde functional grp where H attached to carbonyl C

• R — CHO

• C_nH_2nO

homologous grp with functional grps containing carbonyl grp — ketones

• org compounds with ketone functional grp where 2 alkyl groups attached to carbonyl C

• R — CO — R’

• C_nH_2nO

homologous grp with functional grps containing carbonyl grp — carboxylic acids

• org compounds with carboxyl functional grp (hydroxyl attached to carbonyl C)

• R — COOH

• C_nH_2nO₂

homologous grp with functional grps containing carbonyl grp — esters

• org compounds with ester functional grp (O atom attached to carbonyl C and alkyl C)

• R — COO — R’

• the ester functional grp (-COO-) is called ester link → formed via condensation reaction between hydroxyl and carboxyl functional grps

• name = stem of alcohol part + stem of main chain + oate (e.g. ethyl hexanoate) — note that the main chain must always include that carbonyl C

• C_nH_2nO₂

isomers def

comps same molecular formula but diff atom arrangements

(hence diff chem and physical properties)

structural isomers

same molec formula but atoms arranged diff orders

• chain isomers

• positional isomers

• functional isomers

— diff IUPAC names

chain isomers

struc isomer type where diff atom arrangement order by changed main C chain

positional isomers

struc isomers type where diff atom arrangement order by changed position of functional grp (located on diff C atoms)

functional isomers

struc isomers type where diff atom arrangement order by changed functional grp

• aldehyde and ketone

• carboxylic acid and esters

• alkene and cycloalkane

intermolecular forces

• determines properties of substances

• act between molecs

• influenced by elements, bonds, shapes molecs

• dispersion forces, dipole-dipole attractions, hydrogen bonding

intermolecular forces — dispersion forces

• electrons momentarily distributed unevenly within molecs → temp dipole → neighbouring molecs with similar temp dipoles are attracted weakly with each other → weak dispersion forces between molecs

• for non-polar molecs this is only intermolecular force → determines overall strength intermolecular bonding

• weak and temporary (bc electrons redistribute themselves at diff times)

intermolecular forces — dipole-dipole attractions

• molecs that polar and have permanent dipoles

• partial +ve charge on one molec is electrostatically attracted to partial -ve charge on neighbouring molec

• stronger than dispersion forces

intermolecular forces — Hydrogen bonding

• when hydrogen bonds with F, N, O (highly electronegative atoms) its electrons move slightly towards atom → hence H nucleus exposed → the molec becomes dipole (+ve charge?) → H bonding occurs with this dipole and another molec with an electronegative atom

• stronger than dipole-dipole attractions and dispersion forces (bc small size of H atom → larger dipole moment → molecs can get closer to each other → increased force of attraction

• can occur between water and organic compounds

physical properties def

measurable and used to describe how subs behaves without changing chem composition

physical properties — boiling point and melting point

• depends on strength of intermolecular forces (H bonding > dipole-dipole attractions > dispersion attractions)

• as no. C atoms increase → increase dispersion forces → harder separate molecs → need higher temps

• compounds with longer chain molecs → molecs can arrange closer → increased dispersion forces → increased intermolecular forces → harder separate molecs → higher temps

— the stronger the intermolecular forces, higher the boiling point

intermolecular forces for homologous grps

• DISPERSION ONLY = alkanes, alkenes, alkynes

• DISPERSION, DIPOLE-DIPOLE = haloalkanes, aldehydes, ketones, esters

• DISPERSION, HYDROGEN BONDING = alcohols, carboxylic acids, amines, amides

physical properties — viscosity

• resistance to flow of a liquid

• larger molecs → increased dispersion forces → increased intermolecular forces → higher viscosity

• temp increases → molecs have enough energy to overcome forces holding them tgt → viscosity decreases

— the stronger the intermolecular forces, higher viscosity

physical properties — solubility

• for a subs to dissolve in water → molecs must interact with water → molecs separate so new interactions form

• non-polar molecs cannot interact with water → can be attracted to non-polar solvents via dispersion forces

• polar molecs → slightly soluble bc dipole-dipole attractions with water molecs → can separate so new interactions can form

• molecs most likely dissolve in water are those can form H bonds

• as org compounds molecs size increases → non-polar section of molec increases → solubility decreases

the effects of side-chains or branching on intermolecular force strength

branching amount increases → molecules cannot get as close to each other → as dispersion forces work for small distances, attraction reduced → bp and mp increase

symmetrical branching increases → decreased mp and bp

when explaining physical properties

• use molec structure to justify type of intermolecular forces

• explain how diff in intermolecular bonds results in diff properties

order of homologous grps intermolecular strengths (from highest to lowest)

carboxylic acid > amines / alcohols > esters / ketones / aldehydes / haloalkanes > hydrocarbons

substitution reactions def

one or more atoms on molec replaced by others

ORGANIC REACTIONS — alkane substitution

• 4 strong covalent bonds and non-polar hence relatively unreactive

• halogen can replace one or more H atoms

• must happen under extreme conditions → UV light / heat — breaks covalent bond so reaction can occur

• prod haloalkanes (primary haloalkanes = halogen attached to C atom that only attached one other C atom)

— e.g. halogens are Cl₂, Br₂ (fluorine too reactive, iodine too unreactive)

ORGANIC REACTIONS — haloalkane substitution

• molecs are polar bc electronegative halogens → can be subs with other atoms now (electron-rich grps)

• if sub halog with -OH → prod alcohol

• if sub halog with NH₃ → prod amine

addition reactions def

when one molec bonds covalently with another molec without losing any other atoms

ORGANIC REACTIONS — ALKENE ADDITION

• unsat → weak bond in alkene double bond → can break more easily → new single bonds form and new atoms added

— can occur with:

• hydrogen (needs catalyst like Ni)

• halogen

• HCl

• water (need H₃PO₄ catalyst at 300 degrees C) — note hence water is (g) state as steam

— addition polymerisation can also happen → alkene double bonds broken and each molec joined with others to form long chain (e.g. monomer = ethene, polymer = polyethene)

— note: when react alkene with Br₂ can test for unsaturation as red-brown colour lost as bromine reacts

primary, secondary, tertiary alcohols

• primary = C atom bonded to hydroxyl grp is only bonded to one other C atom (+ 2 other H atoms?)

• secondary = C atom bonded to hydroxyl grp is bonded to 2 other alkyl grps / C atoms (+ one other H atom?)

• tertiary = C atom bonded to hydroxyl grp bonded to 3 other alkyl grps / C atoms

ORGANIC REACTIONS — primary alcohol oxidation

• in presence of oxidant = MnO₄^-/H⁺ , Cr₂O₇^2-/H⁺

• primary alcohol → (loses some H) → aldehyde → (O added?) → carboxylic acid

ORGANIC REACTIONS — secondary alcohol oxidation

• in presence of oxidant = MnO₄^-/H⁺ , Cr₂O₇^2-/H⁺

• secondary alcohol → (loses some H) → ketone

ORGANIC REACTIONS — tertiary alcohol oxidation

• cannot be oxidised (bc can remove H atom easily from C hence cannot form double bond with O)

• can separate primary and secondary alcohols from tertiary → tertiary cannot oxidise → hence Cr₂O₇^2- and MnO₄^- cannot cause colour change for tertiary but can for primary and secondary as they are reacting (orange to green, purple to pink respectively)

reaction pathway def

shows raw materials and sequence of steps needed to synthesise chem product

e.g. factors to choose a particular reaction pathway to manufacture chem products

• cost and availability raw materials

• energy cost

• percentage yield

• atom economy

etc

primary amine synthesis e.g. reaction pathways

• alkane → haloalkane → amine

• alkene → haloalkane → amine

• alkene → alkane → haloalkane → amine

— note that need to conv into haloalkene first bc it’s more reactive → then heat with solution of concentrated ammonia in ethanol → amine mixture prod → separated via frac distillation

carboxylic acid synthesis e.g. reaction pathways (can also then prod ester)

• alkane → haloalkane → alcohol → carboxylic acid (→ ester)

• note: the further down the grp the halogen is — the faster OH replaces it → faster reaction rate

• AH ACE