An Introduction to Organic Chemistry
Dr Sandy Wilkinson [email protected] Aims By the end of this unit students should be able to:
Demonstrate an understanding of the basics of organic chemistry: nomenclature, isomerism and mechanisms
Demonstrate an understanding of the basic chemistry associated with the organic functional groups covered
Apply functional group chemistry to suggest basic organic reaction schemes Texts
J. Smith, “Organic Chemistry”, 5th edition (2017), McGraw-Hill C. E. Housecroft and E. C. Constable, “Chemistry with Mastering Chemistry”, 4th Edition (2009), Prentice Hall P. Atkins, L. Jones and L. Laverman, “Chemical Principles: The Quest for Insight”, 5th edition (2016), W. H.Freeman M. Hornby and J. Peach, “Foundations of Organic Chemistry”, 1997, Oxford University Press Useful Websites…
www.chemguide.co.uk http://www.knockhardy.org.uk/sci.htm Fundamental Principles of Organic Chemistry Electrons occupy ‘orbitals’ which have different energies and shapes. 2py 2s 1s 2pz 6p 6n 2px
2p energy 2s 2 2 1 1 1s 2s 2px 2py
1s Covalent bonds involve pairs of electrons.
H
H C H
H Covalent bonds involve pairs of electrons.
H H
H C H H C H
H H Elements have different electronegativities (χ).
How easily an atom attracts a pair of electrons in a covalent bond.
+ - H Cl
Measured on the ‘Pauling Scale’ – a dimensionless, relative scale. + - + - H Cl C Cl Cl Cl 2.20 3.16 2.55 3.16 3.16 3.16
https://sciencenotes.org/electronegativity-definition-and-trend/ Molecules can have lone ‘pairs’.
H N H O H H H Reactions involve the breaking and making of bonds.
H H
Cl Cl + H C H H Cl + Cl C H
H H Molecules occupy 3D space. Organic Chemistry O
C H
N Urea
Pb(OCN)2 + 2NH3 + 2H2O Pb(OH)2 + 2NH4(OCN)
NH4(OCN) NH3 + HOCN (NH2)2CO Urea
Friedrich Wohler (1828) Organic Chemistry Organic chemistry is concerned with the structure, properties and reactions of ‘organic compounds’.
Organic compounds contain covalently bonded carbon atoms along with other elements such as hydrogen, oxygen, nitrogen and so on.
Organic compounds are used as: Pharmaceuticals (drugs/medicines) Plastics and polymers Food additives (e.g. preservatives, flavours) Agrochemicals Fuel additives
Organic compounds are also involved in life processes. Organic Compounds
Aspirin Ascorbic Acid (Vitamin C)
Ethenylbenzene Cysteine (‘Styrene’) (an Amino Acid) Carbon Chemistry Forms strong covalent bonds with itself and many other elements (e.g. H, O, N, S, Cl) Undergoes Catenation – the ability to bond with the same element to form a series:
Chains
Rings Carbon Forms four covalent bonds which allows branching.
CH3
CH CH3 H3C CH2
Carbon can also form multiple bonds with itself or other elements. Organic Compounds
The carbon ‘skeleton’. The functional group Functional Groups
Group Stem General Formula + Structure Example
Alkane -ane RH C C C2H6 ethane
Alkene -ene C C C2H4 ethene
Alkyne -yne C C C2H2 ethyne
Haloalkane halo- RX C X C2H5Cl chloroethane
Alcohol -ol ROH C OH C2H5OH ethanol
Ether ether ROR C O C C2H5OC2H5 diethyl ether O Aldehyde -al RCHO C CH3CHO ethanal H
C Ketone -one RCOR C O CH3COCH3 propanone C
O Carboxylic Acid -oic acid RCOOH C CH3COOH ethanoic acid OH O Ester -yl -oate RCOOR C CH COOCH methyl ethanoate OR 3 3
O Amide -amide RCONH2 C CH3CONH2 ethanamide NH2
O Acyl Chloride -oyl chloride RCOCl C CH COCl ethanoyl chloride Cl 3 Nitrile -nitrile RCN C N CH3CN ethanenitrile
Amine -amine RNH2 C NH2 CH3NH2 methylamine
Nitro nitro- RNO2 C NO2 CH3NO2 nitromethane Formulae
Empirical Formula - The simplest whole-number ratio of atoms. There is no link between the structure of a molecule and its empirical formula. Different molecules can have the same empirical formula.
Molecular Formula – Shows the all the atoms, and the number of each atom in a molecule for example C3H6O2. For organic compounds, these are written C, then H, then other elements in alphabetical order, for example C4H8BrCl.
H H Empirical Formula: CH3 Ethane H C C H Molecular Formula: C2H6 H H Determining Empirical Formulae from Percentage Composition A compound was found to have a composition of 85.63 % C and 14.37 % H. What is its empirical formula? [Use the following RAMs: C = 12.01, H = 1.008] C H
Divide percentages 85.63 14.37 by RAM 12.01 1.008
7.13 14.25 Divide all by lowest 7.13 7.13
Make sure ratio is in 1 2 whole numbers
EF is CH2 A compound of C, H and O was found to have a composition of 40.00 % C and 6.71 % H. What is its empirical formula? [Use the following RAMs: C = 12.01, H = 1.008, O = 16.00]
C H O 40.00 6.71 53.29 12.01 1.008 16.00
3.33 6.66 3.33 3.33 3.33 3.33
1 2 1
CH2O The compound was found to have a molecular mass between 55-65, what is its molecular formula?
C2H4O2 A compound was found to have a composition of 83.26 % C and 16.38 % H and a molecular mass of 86. What is its molecular formula? C H 83.26 16.38 12.01 1.008
6.93 16.25 6.93 6.93
Make sure ratio is in 2.34 whole numbers – if 1 not, multiply by odd 3 7 numbers(x3, x5 etc.) each until it is.. EF = C3H7
MF = C6H14 An organic compound is made of carbon, hydrogen and oxygen only and contains C 66.63 % and H 11.18 %, the remainder being oxygen. Its Relative Molecular Mass is about 72. Calculate the formula of the compound. [Use the following Atomic Masses, C = 12.01, H = 1.008, O = 16.00]
C H H 66.63 11.18 22.19 12.01 1.008 16.00 5.55 11.09 1.39 1.39 1.39 1.39 4 8 1
EF is C4H8O
MF is C4H8O Determining Empirical Formulae from Combustion Data (Hydrocarbons)
CXHY + excess O2 → X CO2 + (Y/2) H2O
For example:
C8H18 + 12 ½ O2 → 8CO2 + 9H2O A hydrocarbon is combusted with an excess of oxygen yielding
211.2 g of CO2 and 129.6 g of H2O. Give the empirical formula of the hydrocarbon. CXHY + excess O2 → x CO2 + (Y/2) H2O
CO2 H2O Find moles of products -divide 211.2 129.6 masses of products by their RMM 44.01 18.016
4.80 7.19 Divide all by lowest 4.80 4.80
Make sure ratio is in X = 1 Y/2 = 1.5 whole numbers Y = 3
EF is CH3 A hydrocarbon is combusted with an excess of oxygen yielding
8.45 g of CO2 and 1.73g of H2O. Give the empirical formula of the hydrocarbon.
CO2 H2O 8.45 1.73 44.01 18.016
0.192 0.0960 0.0960 0.0960
X = 2 Y/2 = 1 Y = 2
EF is CH Representing Organic Compounds
Molecular formulas (e.g. C3H6O)
Displayed Formula Skeletal Formula
Other Representations https://chem.libretexts.org/Courses/Athabasca_University/Chemistry_350%3A_Organic_Chemistry_I/Chapter_01%3A_Structure_and_Bonding/1.12_Drawing_Chemical_Structures Drawing Molecules in ‘3D’
C-H bonds in the plain of the screen C-H bond behind the plane of the screen
C-H bond projecting in front of the plane of the screen
‘ball and stick’ representation of methane Symbols are used to represent bonds that are in, behind or in front of the plane of the paper (or screen).
‘normal’ bond – represents bonds in the plane wedged bond – represents bonds in front of the plain dashed bond – represents bonds behind the plane
draw the add the two draw the bond add the bond ‘central’ atom bonds in the projecting behind the plain plane forward