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Organic chemistry

Historically - organic molecules could only be produced by living things - "vitalism" - the intervention of a "vital force" was necessary for the synthesis of an organic compound.

-could not be produced in a beaker

-similar to what we now think of with the commercial term "organic"

Of course, many organic compounds can be produced in the laboratory:

Ex: honey that a bee makes (glucose) can be made in the laboratory

What's in a name?

2,3,4,5,6-hexahydroxyhexanal

Often when one sees a "chemical name", it is assumed to be artificial, not "organic"

The above is simply the systematic name for the compound glucose.

Organic compounds are those based primarily on Carbon.  Such compounds dominate our lives.  The majority of "chemical names" we see are organic compounds.  For instance, check out this ingredients list:

a-Terpinolene, Ethyl butanoate, 3-Carene, Ethyl acetate, Ethyl 2-butenoate, a-Terpinene, a-Thujene, Dimethyl sulfide, Limonene, b-Phellandrene, Myrcene, p-Cymen-8-ol, b-Caryophyllene, cis-3-Hexene-1-ol, hexadecyl acetate, 5-Butyldihydro-3H-2-furanone, trans-2-hexenal, Ethyl tetradeconaoate, a-Humulene, Ssabinene, 2-Carene, Camphene, Ethyl octanoate, 4-Isopropenyl-1-methylbenzene 1-Hexanol, g-terpinene, hexanal, Ethyl hexadecanoate, a-Copaene, Hexadecanal, Ethanol, Ethyl propionate, Dihydro-5-hexyl-3H-2-furanone, Carveol, Geranial, Ethyl decanoate, Furfural, Butyl acetate, Methyl butanoate, 2,3, Pentanedione, 1,1, diethoxyethane, pentadecanal, Butyl formate, 1-Butanol, 5-Methylfurfural, Ethyl dodecanoate, 2-Acetylfuran, 2 Methyl-1-butanol, 4-Methylacetophenoen, Acetaldehyde, Cyclohexane

From: The extraordinary chemistry of ordinary things, C.H. Snyder

 

 

 

 

ingredients list above is a partial list for the Mango

Bonding to carbon

1. organic compounds are generally made up of carbon bonded to other non-metals - covalent bonding is expected

2. Lewis structure of carbon important in understanding bonding

To satisfy octet rule, carbon will often bond to four other things

Remember methane CH4

pdb model

 

Bonds get as far as part as possible - tetrahedral

hydrogen can only form a single bond with another atom such as carbon

A closer look at the bonding in methane:

Covalent bonds represent the sharing of electrons -  we drew pictures of orbitals on atoms (s,p,d,f) - can we imagine how they are shared to form bonds??

For H2, this is simple:

How about for methane: CH4

Electron configuration of C = 1s22s22p2

If we imagine the valence p and s orbitals, it is hard to see how we get tetrahedral bonding because these orbitals do not point to the corners of a tetrahedron.

Answer: orbital hybridization - the s and p orbitals merge to form four new orbital called  sp3 hybrids.  The sp3 nomenclature indicates that the orbitals formed are 25% in s-character and 75% in p-character.  The four sp3 orbitals formed point to the corners of a tetrahedron.  

The bonding in  methane can then be seen as the overlap of the s-orbitals of hydrogen and the sp3 hybrid orbitals of carbon.  Remember, angle between bonds is 109.5o

Hydrocarbons

dominant elements in organic molecules are carbon and hydrogen: 

molecules which contain only carbon and hydrogen are called hydrocarbons:

Note: Study Fig 11.4 to better understand the ways in which structural formulas are drawn.

1-carbon

methane

gas - natural gas

2-carbons

ethane

or      or  

gas

3-carbons

propane

  or CH3CH2CH3 or C3H8

gas - barbecues

4-carbons

butane

CH3CH2CH2CH3  or C4H10

gas - lighter fluid

5-carbons

pentane

C5H12

liquid

6-carbons

hexane

C6H14

liquid

7-carbons

heptane

C7H16

liquid

8-carbons

octane

C8H18

liquid

9-carbons

nonane

C9H20

liquid

10-carbons

decane

C10H22

liquid

All of the above compounds containing all C-C single bonds are called alkanes, which have the general forumula:

CnH2n+2

mineral oil: C16 - C20

petroleum jelly and waxes: >C20 - C25

Shapes of alkanes - tetrahedra bound together leads to zig/zag shapes.  

Different "conformations" are possible due to rotations about C-C bonds (see fig 11.5 in book and see pdb models above).  Compare two conformations of butane: the "anti" conformation, and the "eclipsed" conformation.

Isomers

Alkanes and organic molecules in general can exist as isomers

isomers - molecules that have the same chemical composition (chemical formula) but different molecular structures

ex.  C4H10 - can arrange 4 carbons and 10 hydrogens in more than one way and still have the octet rule satisfied - 2 isomers

butane

=

isobutane

 

ex: pentane C5H12 - 3 isomers

pentane

isopentane

neopentane

C10H22 has 75 isomers

C20H44 has 366,319 isomers