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Organic Chemistry

Learn about the fundamentals of organic chemistry, including the definition of organic compounds, the unique properties of carbon, and the importance of organic chemistry in biochemistry. Explore different families of organic compounds and the general trends in their physical properties.

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Organic Chemistry

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  1. Organic Chemistry • What do we mean by “organic” chemistry? • What do the following things below have in common?

  2. Organic-dictionary definition • Oxford English dictionary says: • “organic” means derived from living matter, i.e. not produced artificially • For example, “organic food” refers to the food that is produced without the use of chemical fertilisers, pesticides or other artificial chemicals.

  3. Organic- chemical definition • Of all the elements in the periodic table, one is much more versatile (stands out) from the rest • Carbon can form more compounds than any other element • Chemical definition: Organic chemistry is the study of compounds containing carbon (other than simple binary compounds and salts) and chiefly or ultimately of biological origin. • Question: Is carbon itself organic or inorganic?

  4. Carbon-revisited hopefully! • In group 4 of the periodic table • Electronic configuration: 2,4 (SL) or 1s2 2s2 2p2 (HL) • Has a valency (combining power) of 4 with 4 valence (outer shell) electrons • Achieves the noble gas configuration of neon by forming 4 covalent bonds • Take methane for example: carbon is bonded covalently to 4 hydrogen atoms to achieve its octet

  5. Carbon- continued • The valency of 4 gives rise to a unique property called catenation • Catenation: spontaneous linking of atoms of certain chemical elements, such as carbon atoms, to form long chains or stable rings by forming covalent bonds with itself • C-C bond enthalpy = 348 kJ mol-1 • C-H bond enthalpy = 412 kJ mol-1 • Catenation allows billions of organic compounds to be formed • Carbon compounds > ∑ all other compounds of all the elements in the periodic table except hydrogen (since almost all organic compounds also contain hydrogen) • 7 million Organic Compounds • 1.5 million Inorganic Compounds

  6. Organic chemistry- link to nature • Life is based on organic compounds • The 4 major classes of biomolecules are all organic (contain carbon) • Carbohydrates, Proteins, Lipids & Nucleic Acids • Organic chemistry is an excellent foundation for biochemistry • Biochemistry is just APPLIED organic chemistry! • Just like physics is applied maths!

  7. Hydrocarbons • A compound which consists of carbon & hydrogen ONLY • Are the basis for most organic compounds • Includes alkanes, alkenes, alkynes (aliphatic compounds), & arenes (aromatic compounds)

  8. Organic compound families- homologous series • Can be grouped into different families with a common functional group (part of the molecule which gives rise to common reactivity) • Homologous series: a group of organic compounds that follow a regular structural pattern and have the same general molecular formula, differing only by the addition of a methylene, -CH2- group, they have almost identical chemical properties, with physical properties e.g. boiling point increasing gradually as the number of carbon atoms increase

  9. Homologous series • Take the alkanes for example: • The 1st 4 are methane, ethane, propane, butane

  10. Homologous series- properties • Successive compounds differ from each other by a -CH2- unit (methylene group) • The compounds can all be represented by a general formula (e.g. alkanes CnH2n+2; if n=3 then the formula is C3H8 • The compounds have similar chemical properties • Successive compounds have physical properties that vary in a regular manner as the number of carbon atoms increases

  11. Homologous series- general trends in physical properties • For the alkanes: As the number of carbon atoms increase the melting/boiling points gradually increase • This is caused by an increase in the molar mass of the molecule and hence there is greater chance of more temporary dipoles being induced in the case of hydrocarbons (Van der Waals forces)

  12. Graph of boiling points for the first 10 alkanes • Curve is initially quite steep, as for small molecules, the addition of an extra carbon has a proportionally larger effect on the molar mass (eg, from CH4 to C2H6 there is an increase of 97.5%) & hence on the strength of the van der Waals’ forces • As the length of the carbon chain increases, the percentage change in molar masses becomes progressively smaller (there is a 10.9% increase in molar mass from C9H20 to C10H22, hence the curve flattens • The trend is the same for other physical properties, such as density & viscosity for the same reasons

  13. Empirical, molecular, structural (condensed & full) formulae • Using ethane, C2H6, as an example • Empirical formula: simplest whole number ratio of atoms e.g. CH3 • Molecular formula: actual number of atoms of each type present in a molecule e.g. C2H6 • Full structural formula: show the relative positioning of all the atoms in a molecule & the bonds between them • Condensed structural formula: omits bonds which can be assumed & groups atoms together e.g CH3CH3

  14. Shapes of Alkanes • “Straight-chain” alkanes have a zig-zag orientation in 3-D

  15. Formulae- worked example • Write the empirical, molecular, full structural & condensed structural formula for ethanol, CH3CH2OH Answer: • Empirical: C2H6O • Molecular: C2H6O • Full structural:

  16. Further functional groups • Alkenes: CnH2n e.g. ethene C2H4 • Alkynes: CnHn e.g. ethyne C2H2 • Alcohol: CnH2n+1OH e.g. methanol CH3OH • Aldehydes: RCHO, e.g. methanal (formaldehyde) HCHO • Ketones: RCOR’ (R’ can be the same alkyl group as R or different e.g. propanone (acetone), CH3COCH3 • Carboxylic acids: RCOOH, e.g. methanoic (formic) acid, HCOOH • Haloalkanes: RX (X=F,Cl,Br,I) e.g. iodomethane, CH3I • Amines: RNH2 e.g. methylamine, CH3NH2 • Esters: RCOOR’ e.g. methyl methanoate HCO2CH3 • Arenes: based on the phenyl group (C6H5-) e.g. benzene C6H6

  17. Isomers • Compounds with the same molecular formula but with different arrangement of atoms in the molecule • For the alkanes: from butane (4 carbon atoms), there is more than 1 structure possible • C4H10 can refer to either butane, CH3CH2CH2CH3 or methylpropane, CH3CH(CH3)CH3

  18. Isomers

  19. Structural Isomers • Different connectivity of atoms E.g.: • Butane & methylpropane are structural isomers of each other • 3 types: • Chain isomerism • Position isomerism • Functional group isomerism

  20. Chain isomerism • Different arrangement of the carbon skeleton • For example butane & methylpropane are chain isomers of each other • Have similar chemical properties but different physical ones; the branched isomer has a lower melting/boiling point than the straight-chained one CH3 H H H H H H H H H C C C C C H C C methylpropane butane H H H H H H H

  21. Position Isomerism • Have functional group placed at a different position along the carbon skeleton • E.g. 1-bromopropane & 2-bromopropane • Has similar physical & chemical properties Br H Br H H H H H H H C C C C C C 2-bromopropane 1-bromopropane H H H H H H

  22. Functional group Isomerism • The molecules have different functional groups (hence different chemical properties) • E.g. ethanol & methoxymethane all have the same molecular formula of C2H6O, however ethanol is an alcohol while methoxymethane is an ether ethanol methoxymethane

  23. Naming organic compounds • International Union of Pure & Applied Chemistry (IUPAC) devised nomenclature method • It is irregular for up to 4 carbon atoms, just have the prefixes meth-, eth-, prop-, but- • From 5 carbon atoms & above the naming becomes systematic, like those of geometrical shapes, e.g. pent- (pentagon), hex- (hexagon), hep- (heptagon), oct- (octagon) etc • The name of any organic compound is usually made up of 3 parts: prefix (substituents), stem(number of carbon atoms in main chain) & suffix(homologous series of main carbon chain) • e.g. methylpropane methyl- CH3 substituent prop- 3 carbon atoms in main chain -ane- belongs to the alkane homologous series

  24. Monkeys • Eat • Peeled • Bananas Mimic for first four prefixes

  25. Counting to Ten in Organic • 01 = meth Mother • 02 = eth Enjoys • 03 = prop Peanut • 04 = but BUTter • 05 = pent PENTagon • 06 = hex HEXagon or HEX nut • 07 = hept HEPTember (Roman sept is Greek hept) • 08 = oct OCTober • 09 = non NONember (Roman nov is Greek non) • 10 = dec DECember

  26. Naming side chains • If there are alkyl groups (R groups) attached in isomers, the prefix for the alkyl groups must be used

  27. Steps in naming alkanes- step 1 For the molecule CH3CH(CH3)CH(CH3)CH3 Identify the longest continuous carbon chain (This may not be the most obvious, straight one), this gives the stem, given by the 4 blue carbon atoms

  28. Steps in naming alkanes- step 2 CH3CH(CH3)CH(CH3)CH3 • Identify & name the side-chains/substituent groups as the prefix of the name. • Here there are 2 different methyl groups

  29. Steps in naming alkanes- step 3 CH3CH(CH3)CH(CH3)CH3 • Where there is more than 1 side-chain of the same type, like here, use the prefixes di-, tri-, tetra- and so on, to indicate this. • If there are several side-chains within a molecule, put them in alphabetical order, seperated by dashes. • There are 2 methyl groups- hence the prefix is dimethyl

  30. Steps in naming alkanes- step 4 1CH32CH(CH3)3CH(CH3)4CH3 • Identify the position of the side chains. • The carbon chain is numbered from the end which will give the substituent groups the smallest number. • Here 1 methyl group is attached to carbon number 2; the other to carbon number 3. • The numbers precede the name and each digit is separated by a comma from the next digit • Hence the name of this compound is 2,3-dimethylbutane

  31. Some exercises H • Name the following compound: H C H H H H H C H C C C C H H H H H C H H H C H H

  32. Step 1- Find the longest carbon chain H H C H H H H H H C C C C C H H H H H H C H H C H H

  33. Step 2- Look for any substituents attached H 2 methyl groups H C H H H H H H C C C C C H H H H H H C H H C H H

  34. Steps 3 & 4- Find the location of the substituents to give the lowest possible overall number H Hence green is correct 2 methyl groups H C H H H H H Using the green numbering gives the lower substituent number of 3,3-dimethylhexane C H C C C C H 3 4 5 6 2 H 4 H 3 1 H H H C H Using the orange numbering gives the higher substituent number of 4,4-dimethylhexane 5 2 H C H 1 6 H

  35. Answer H • Hence the name of the molecule is 3,3-dimethylhexane H C H H H H H C H C C C C H H H H H C H H C H H H

  36. Isomers of C4H10- IUPAC vs common name Methylpropane methylbutane dimethylpropane IUPAC common

  37. Some well know molecules - IUPAC vs common name IUPAC: 2,3,5,4,6-Pentahydroxyhexanal Common: glucose IUPAC: 3-carboxy-3-hydroxypentanedioic acid Common: citric acid

  38. Alkene isomers • Have the general formula CnH2n • Have the C=C functional group within the chain • Simplest alkene is ethene, C2H4 • If molecule is longer than 3 carbon chains, the double bond can be in more than 1 position ethene propene

  39. Naming alkene isomers • Same 1st 4 steps as alkanes except the name (suffix) ends in -ene instead of -ane • Step 5- The position of the double bond C=C is shown by inserting the numb er of the carbon atom at which C=C starts • E.g. for the isomers of C4H8 • CH3CH2CH=CH2 is but-1-ene • CH3CH=CHCH3 is but-2-ene • CH2=C(CH3)2 is 2-methylprop-1-ene

  40. Practice problem • What is the name of the following alkenes: • CH3CH=CHCH2CH2CH3 • CH3CH2CH(CH3)CH=CH2 • CH2=C(CH3)CH2CH=CH2 Answer: • hex-2-ene • 3-methylpent-1-ene • 2-methylpent-1,4-diene

  41. Naming alcohols (ROH) • Always end in –ol • Simplest is methanol • Like alkenes, the position of the –OH group must be specified after ethanol • e.g. • CH3CH2CH2OH is propan-1-ol • CH3CH(OH)CH3 is propan-2-ol ethanol Propan-1-ol Propan-2-ol

  42. Practice problems • Name the following alcohols: 1) CH3C(OH)(CH3)CH2CH2CH3 2) Answers 1)2-methylpentan-2-ol 2) propan-1,2,3-triol

  43. Naming aldehydes (RCHO) • Always end in –al NOT (ol)! • Simplest is methanal • -CHO group is always at the end, so this carbon must be carbon 1 so unnecessary to specify location • E.g. methanal propanal ethanal

  44. Practice problems • Name the following aldehydes: • CH3CH2CH2CHO 2) HCOCH2 CH2CH3 • Answer: • butanal • butanal

  45. Naming ketone (RCOR’) • Always ends in suffix –one • Simplest is propanone (acetone) • The C=O (carbonyl) group can be inserted anywhere along the hydrocarbon chain except at the end (why?) • After butanone, the position of the carbonyl group must be shown • E.g pentan-2-one & pentan-3-one propanone butanone

  46. Practice problems- ketones • Name the following ketones: 1) CH3COCH2CH2CH2CH3 2) CH3CH2CH2COCH3 OC CH3 CH2CH2CH3 • Answer: • hexan-2-one • pentan-2-one • pentan-2-one

  47. Naming carboxylic acid (RCOOH) • End in –oic acid • Like aldehydes, COOH is always the terminal group & hence this carbon is always carbon number 1 Ethanoic (acetic) acid Methanoic acid Propanoic acid

  48. Practice problems- carboxylic acids Name the following carboxylic acids: • CH3CH2CH2CO2H • HOOCCH2CH2CH3 • CH3CH2CH(CH3)CH2COOH Answer: • butanoic acid • butanoic acid • 3-methylpentanoic acid

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