Organic Chemistry

Periodic Table has 118 elements. Let’s look at some «Organic» Molecules

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Periodic Table for these Organic Molecules ?

Organic Chemistry  The chemistry of life  The study of Carbon (C)  More specifically, the study of the bonds formed between Carbon (C) and (mostly):  Hydrogen (H),  Oxygen (O)  Nitrogen (N).

Valency  Number of bonds formed determined by atomic structure  Remember:  A covalent bond is formed when two atoms share a pair of electrons!  Covalent bonds of Carbon form the basis of Org Chem

Valency  Sharing 1 pair of electron = single bond  Sharing 2 pairs of electrons = double bond  Sharing 3 pairs of electrons = triple bond  Different atoms can form different amounts of bonds  Why?

Valency - H  Look at atomic structure  H is atom no. 1  No. of protons: 1  No. of electrons: 1  1 electron means it can form only 1 covalent bond (EVER!) 1 s 2 2 s 2 p 6 3 s 2 p 6 d 10 4 s 2 p 6 d 10 f 14

Valency - H  Look at atomic structure  H is atom no. 1  No. of protons: 1  No. of electrons: 1  1 electron means it can form only 1 covalent bond (EVER!)

Valency - C  C : element number 6  => 6 protons and 6 electrons  Electronic configuration: 1s 2, 2s 2, 2p 2  1s electrons not involved in bonding so 4 valence electrons (v.e -.)  Octet rule: C wants 8 electrons  Must share all 4 electrons to get 8 1 s 2 2 s 2 p 6 3 s 2 p 6 d 10 4 s 2 p 6 d 10 f = 8

Valency - C  C must form 4 bonds to form stable compounds  Can be any combination of single, double and triple bonds  Can NEVER exceed 4 bonds around a C atom

Valency - O  Electronic structure: 1s 2, 2s 2, 2p 4  6 valence electrons available  Wants 8 so only needs 2 more  O can form 2 bonds; valency = 2  This means 1 double bond or 2 single bonds 1 s 2 2 s 2 p 6 3 s 2 p 6 d 10 4 s 2 p 6 d 10 f = 8

Valency - O  Electronic structure: 1s 2, 2s 2, 2p 4  6 valence electrons available  Wants 8 so only needs 2 more  O can form 2 bonds; valency = 2  This means 1 double bond or 2 single bonds 1 s 2 2 s 2 p 6 3 s 2 p 6 d 10 4 s 2 p 6 d 10 f = 8

Valency - N  Electronic structure: 1s 2, 2s 2, 2p 3  5 valence electrons available  Wants 8 so only needs 3 more  N can form 3 bonds; valency = 3  This means 3 single bonds; 1 double bond and 1 single bond or 1 triple bond. 1 s 2 2 s 2 p 6 3 s 2 p 6 d 10 4 s 2 p 6 d 10 f = 8

This gives functional groups... Carbon Nitrogen Oxygen

Drawing Organic Compounds  Molecular Formula: tells exactly how many of each atom is present; Shorthand notation  Tells nothing about how they are connected  Structural Formula: Longhand; shows which atoms are connected to which.

Drawing Organic Compounds  Consider simplest organic molecule: Methane (natural gas)  Molecular formula = CH 4  Only 1 way they can be connected  Methane is an Alkane, a compound which possesses only C and H single bonds

Drawing Organic Compounds  Next alkane is Ethane  Molecular Formula: C 2 H 6  Structural Formula:

Drawing Organic Compounds  Lets skip ahead a bit;  Pentane: C 5 H 12  Looks very messy (and this is still a very simple compound)  Too complicated to draw all molecules like this

Drawing Organic Compounds  Easier method: Draw C-C bonds as lines. Whenever line ends (changes direction), that’s a C atom  Don’t draw in H atoms. Can work out how many are present by subtracting number of bonds visible from 4. Implicit Hydrogens. Vs.

Isomers  Molecules can have the same molecular formula but different structural formulas  Many possible ways to connect atoms  5 carbon alkane: C 5 H 12  3 possible isomers

Isomers  Same molecular formula; different structural formula  Can have very different properties and reactivity  Chemically distinct molecules

Naming Organic Molecules  For alkanes its very easy  Count how many C atoms in longest straight chain. Find corresponding prefix (next slide).  Identify any side groups off major chain. Indicate their positions with lowest possible number.  If all C-H single bonds then alkane. Suffix = ane

Naming Organic Molecules No. of C atoms NameFormula Name of side group 1 Methane CH 4 Methyl 2 Ethane CH 3 CH 3 Ethyl 3 Propane CH 3 CH 2 CH 3 Propyl 4 Butane CH 3 CH 2 CH 2 CH 3 Butyl 5 Pentane CH 3 CH 2 CH 2 CH 2 CH 3 Pentyl 6 Hexane CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Hexyl 7 Heptane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Heptyl 8 Octane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Octyl 9 Nonane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Nonyl 10 Decane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Decyl If more than one side group present use di (2), tri (3) or tetra (4) to show how many

Our isomers of C 5 H 12  Longest chain = 5 C atoms  C5 = pent  No branching  Alkane  Alkane = -ane  Pentane

Our isomers of C 5 H 12

 Longest chain = 4 C atoms  4 = butane  One branching group of 1 C unit = methyl group  It’s on Carbon no. 2 so name is 2-methylbutane  Numbers and letters are always separated by a hyphen (-)

(Carbon) 2 methyl C4 - but alkane 2-methylbutane

Our isomers of C 5 H 12  Can we number any other way?  Longest chain = 4 C atoms  4 = butane  One branching group of 1 C unit = methyl group  It’s on Carbon no. 3 so name is 3-methylbutane  WRONG!! Must have lowest possible number for side chain

Our isomers of C 5 H 12

(Carbon) 2 Methyl + methyl dimethyl C3 - prop alkane 2,2-dimethylpropane

Our isomers of C 5 H 12  Longest chain = 3 C atoms  3 = propane  Two branching groups of 1 C unit = 2 methyl groups  Both on Carbon no. 2 so name is 2,2-dimethylpropane

Multiple bonds  Alkanes are saturated compounds, all single bonds  If 1 or more double or triple bond present then molecule is unsaturated  Molecules with a double bond are called alkenes  Molecules with a triple bond are called alkynes

More naming, more than just single bonds  Naming ALKENES Similar to alkanes  Select longest chain containing the multiple bond. Indicate location of multiple bond.  Identify any side groups.

More naming  Similar to alkanes  Select longest chain containing the multiple bond. Indicate location of multiple bond.  Identify any side groups.

(Carbon) 3 C2 - ethyl C5 - pent alk-1-ene at C1 3-ethylpent-1-ene

More naming  Similar to alkanes  Select longest chain containing the multiple bond. Indicate location of multiple bond.  Identify any side groups. 3-ethylpent-1-ene 2-methyl-5-ethyloct-3-yne

Why?  IUPAC naming standardises naming among all chemical scientists. Therefore we can all be on the same page...  (2α,4α,5β,7β,10β,13α)-4,10-Bis(acetyloxy)-13- {[(2R,3S)-3-(benzoylamino)-2-hydroxy-3- phenylpropanoyl]oxy}-1,7-dihydroxy-9-oxo-5,20- epoxytax-11-en-2-yl benzoate  Taxol