Organic Compounds and Functional Groups. There are more than 19 million known organic compounds,...
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Transcript of Organic Compounds and Functional Groups. There are more than 19 million known organic compounds,...
![Page 1: Organic Compounds and Functional Groups. There are more than 19 million known organic compounds, each with its own physical and chemical properties. This.](https://reader035.fdocuments.us/reader035/viewer/2022062719/56649ed35503460f94be2bbe/html5/thumbnails/1.jpg)
Organic Compounds and Functional Groups
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• There are more than 19 million known organic compounds, each with its own physical and chemical properties.
• This is very daunting, but organic compounds may be classified into families according to their structures.
• Members of the same families tend to have similar properties, so grouping compounds into families helps simplify what would initially seem to be an bewildering number of compounds.
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• Organic compounds are classified and grouped according to what functional groups they contain.
• A functional group is simply a group of atoms which is chemically reactive.
• In general, a functional group either contains a π bond or an electronegative or an electropositive atom(s).
• So the presence of π bonds or polar bonds is a good indicator of chemical reactivity.
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• A given functional group will undergo the same kinds of chemical reactions in most molecules in which they are present.
• The molecule may be very small and simple, or it may be large, complex, and bulky: but the common functional group will behave in an almost identical manner.
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Common Functional Groups• The following table contains many of the
common functional groups which organic molecules may contain.
• Note that in the Table, R is used to signify an alkyl group, a group which contains only sp3 C atoms and H atoms. When more than one R is present in a General Formula, they may or may not be different alkyl groups.
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Common Functional Groups• What are you responsible for?
• You should recognize alkenes, alkyl halides, alcohols, amines, ethers, carboxylic acids, ketones, aldehydes, esters, and amides.
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Functional Groups with a C-C π Bond
• There are several common groups which contain a π C-C bond.
• What is a σ bond? What is a π bond?• Alkenes contain a double bond, while
alkynes contain a triple bond.
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Functional Groups, Cont.
• Arenes, where benzene is the simplest example, are 6-membered rings with alternating single and double bonds (this is a simplistic explanation, arenes have resonance structures).
• Although you know that double and triple bonds are shorter and stronger than single bonds, the π bond is still chemically active and can undergo certain chemical reactions.
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Functional Groups with Carbon Singly Bonded to an Electronegative Atom
• Carbon is quite commonly bonded to an electronegative atom like O, N, Cl, Br, I, F, or S.
• Alkyl halides have C bonded to a halogen; ethers, alcohols have C bonded to O; amines have C bonded to N; and thiols have C bonded to S.
• In all of these cases, the end result is a polar bond with the C having a δ+ charge. This partial charge separation leads to chemical reactivity.
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Carbonyl Functional Groups
• There is a common class of compounds where a C atom is double bonded to O, or the C=O group.
• It’s generic name is the carbonyl group.
• Common carbonyl compounds include amino acids, fatty acids, and soaps.
• There are several types of carbonyl compounds as seen in the Table.
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Carbonyl Functional Groups
– carboxylic acids– esters (sweet smelling compounds found in
fruits, etc., and used in perfumes)– ketones– aldehydes (usually foul smelling like
formaldehyde)– amides (peptides and proteins are amides)
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Carbonyl Functional Groups
– acid halides– acid anhydrides – In all of these groups, the C=O bond is polar
with the O atom having a δ- charge and the C atom having a δ+ charge.
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Properties of Alkanes
• Alkanes are hydrocarbons (C, H compounds) which contain only sp3 hybridized C atoms.
• Thus, they contain only single bonds.• Because of this, they are also called
saturated hydrocarbons, as they are saturated with hydrogen.
• They have a CnH2n+2 general formula (except cycloalkanes).
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Properties of Alkanes
• In general, alkanes are not very reactive.• They will react with oxygen, halogens, and a few
other substances. • Alkanes are common fuel sources for cars, houses,
etc.• Common alkane fuels are methane, propane,
butane, and of course think of your octane rating at the gas pump!
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Properties of Alkanes
• When an alkane (or any hydrocarbon) combusts, the two ideal products are carbon dioxide and water, although carbon monoxide and other unwanted products are made as well.
• Of course, combustion reactions are exothermic, so a great deal of useful heat is given off as well.
• This heat is called the heat of combustion, ΔHcomb.• As you might expect, as you increase the number
of C atoms in the alkane, there is more to burn, and more heat is given off.
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Alkane Halogenation
• Alkanes also react with halogens in a reaction called halogenation.
• UV light acts as a catalyst in starting the reaction.
• One or more halogen atoms may be added to the alkane, so there are a variety of products made.
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Polarity and Intermolecular Forces
• Alkanes are nonpolar molecules as they contain only C-C and C-H single bonds.
• So the intermolecular forces acting between molecules are weak London Dispersion Forces.
• As you may remember, London Dispersion Forces get stronger as the molar mass or molecule size increases.
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London Forces & BPt and MPt• alkanes with a carbon chain up to 4 are gases at
room temperature
• alkanes with a C chain of up to 17 are liquids
• alkanes with a C chain of over 17 are solids.
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London Forces & Molecular Shape• You may also remember, that the bulkiness or shape of the
molecule also affects the strength of the London Dispersion Forces.
• The closer 2 or more molecules may come together, the stronger the London Forces will be, so the higher the boiling and melting point.
• So if a molecule is very bulky with lots of alkyl group branching, molecules can’t get as close together.
• Continuous-chain hydrocarbons have higher boiling and melting points than do what we call branched-chain alkanes.
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Alkane Solubilities
• Because alkanes are nonpolar, they are not very soluble in water or other very polar solvents.
• Instead, they are soluble in relatively nonpolar solvents like benzene, ethers, etc.
• The densities of alkanes are lower than water, which you should know as oil and gas float on water!
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Cycloalkanes
• Cycloalkanes are ring structure where there are no end C; or you could say that the two end C have joined to form a ring.
• Because of this extra C-C bond, 2 H atoms are lost, so the general formula is CnH2n.
• But, just like alkanes, they contain only sp3 hybridized C atoms.
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Properties of Cycloalkanes
• The properties of cycloalkanes are very similar to those of alkanes.
• However, if you use a molecular model kit and make some cycloalkanes, you will notice a few differences.
• Cycloalkanes, particularly small cycloalkanes, are highly symmetric.
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Properties of Cycloalkanes
• You should also notice that cycloalkanes do not rotate around C-C bonds as freely as regular alkanes.
• In open-chain alkanes, there is free rotation around all of the C-C bonds.
• But in cycloalkanes, this C-C rotation is greatly hindered by the closed ring: if there were free rotation around the C-C bond, the ring might be broken.
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Properties of Cycloalkanes
• The smallest cycloalkanes, C3 to C6 or C7, have rigid rings with little C-C rotation possible.
• Because of this rigidity, these rings are strained, and they are more reactive than larger rings.
• As cycloalkanes get larger, the rigidity of the ring decreases, the ring strain decreases, and there is more freedom of rotation.
• Large cycloalkanes are floppy, and are virtually identical to open-chain molecules.
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Properties of Cycloalkanes
• Because of their greater symmetry and hindered C-C rotation, cycloalkanes generally have higher melting points, boiling points, and densities than open-chain alkanes.
• See the following Table for examples.
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Compound B.Pt. M.Pt. Density (g/mL)
Pentane (C5H12)
36.1 -129.8 0.5582
Cyclopentane (C5H10)
49.3 -93.9 0.7457
Octane (C8H18)
125.7 -56.8 0.7026
Cyclooctane (C8H16)
150.0 14.3 0.8349
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