Organic Functional Groups - PowerPoint PPT Presentation

1 / 54
About This Presentation
Title:

Organic Functional Groups

Description:

However, many organic molecules possess other ... They may be aliphatic or aromatic. Aromatic Groups ... Functional Groups on unsaturated aliphatic hydrocarbons ... – PowerPoint PPT presentation

Number of Views:271
Avg rating:3.0/5.0
Slides: 55
Provided by: chip6
Category:

less

Transcript and Presenter's Notes

Title: Organic Functional Groups


1
Organic Functional Groups
2
Functional Groups
  • A functional group is an atom or a group of atoms
    with characteristic chemical and physical
    properties. It is the reactive part of the
    molecule.
  • Most organic compounds have CC and CH bonds.
    However, many organic molecules possess other
    structural features
  • Heteroatomsatoms other than carbon or hydrogen.
  • ? Bondsthe most common ? bonds occur in CC and
    CO double bonds.
  • These structural features distinguish one organic
    molecule from another. They determine a
    molecules geometry, physical properties, and
    reactivity, and comprise what is called a
    functional group.

3
Hydrocarbons are compounds made up of only the
elements carbon and hydrogen. They may be
aliphatic or aromatic.
4
Aromatic Groups
  • Aromatic hydrocarbons are so named because they
    have strong characteristic odors.
  • The simplest aromatic hydrocarbon is benzene. The
    six-membered ring and three ? bonds of benzene
    comprise a single functional group.

5
Functional Groups
6
Functional Groups
  • Ethane This molecule has only CC and CH bonds,
    so it has no functional group. Ethane has no
    polar bonds, no lone pairs, and no ? bonds.
    Consequently, ethane and molecules like it are
    relatively unreactive.
  • Ethanol This molecule has an OH group attached
    to its backbone. This functional group is called
    a hydroxy group. Ethanol has lone pairs and polar
    bonds that make it reactive with a variety of
    reagents.
  • The hydroxy group makes the properties of ethanol
    very different from the properties of ethane.

7
Alkyl Groups
  • Alkyls are alkane side chains or alkane like
    substituents on an organic molecule
  • Alkyls are nonpolar groups
  • Alkyls
  • Methyl -CH3 (Me-)
  • Ethyl -CH2CH3 (Et-)
  • n-butyl -(CH2)3CH3 (nBu-)

8
Functional Groups on unsaturated aliphatic
hydrocarbons
  • Vinylic substituents Allylic substituents
  • Enol Allylic alcohol
  • Enol ether Allylic ether
  • Enamine

R Alkyl
9
Functional Groups on Aromatic hydrocarbons
  • Phenol
  • Aniline

10
Examples of Molecules Containing C-O ? Bonds
Polycyclic ether
11
Carbonyls
  • Compounds Containing the CO Group
  • This group is called a carbonyl group.
  • The carbonyl group contains a polar CO ? bond
    and a C-O ? bond that is more easily broken than
    a CO ? bond.

12
Carbonyls (R)2CO
13
Functional groups in Biomolecules
  • Biomolecules are organic compounds found in
    biological systems.
  • There are four main families of small molecule
    biomolecules
  • amino acids, simple sugars, lipids and
    nucleotides
  • Biomolecules often have several functional groups.

14
Molecules Containing Multiple Functional Group
15
Functional Groups
It should be noted that the importance of a
functional group cannot be overstated.
A functional group determines all of the
following properties of a molecule bonding and
shape chemical reactivity type and strength
of intermolecular forces physical
properties nomenclature Bioactivity
16
Reactivity with Unsaturated Functional Groups
  • Heteroatoms and ? bonds confer reactivity on a
    particular molecule.
  • Heteroatoms have lone pairs and create
    electron-deficient sites on carbon.
  • ? Bonds are easily broken in chemical reactions.
    A ? bond makes a molecule a base and a
    nucleophile.

17
Influence of Functional Groups on Reactivity
  • Recall that
  • Functional groups create reactive sites in
    molecules.
  • Electron-rich sites react with electron poor
    sites.
  • All functional groups contain a heteroatom, a ?
    bond or both, and these features create
    electron-deficient (or electrophilic) sites and
    electron-rich (or nucleophilic) sites in a
    molecule. Molecules react at these sites.

18
Nucleophiles (Nu-) or (Nu) Lewis Bases can act
as Nucleophiles
19
Alkene (Lewis base) reacting with an Electrophile
For example, alkenes contain a C-C double bond,
an electron-rich functional group with a
nucleophilic ? bond. Thus, alkenes react with
electrophiles E, but not with other electron
rich species like nucleophiles (e.g. OH or Br).
20
Nucleophile Attacking an Electrophile
Alkyl halides possess an electrophilic carbon
atom, so they react with electron-rich
nucleophiles.
21
Intermolecular Forces Organic Molecules
22
Ionic Interactions Exist in Ionic
Compounds Ion-Ion Interaction
  • Ionic compounds contain oppositely charged
    particles held together by extremely strong
    electrostatic inter-actions. These ionic
    inter-actions are much stronger than the
    intermolecular forces present between covalent
    molecules.

23
Intermolecular Forces Between Molecules
  • Intermolecular forces are also referred to as
    noncovalent interactions or nonbonded
    interactions.
  • The nature of the forces between molecules
    depends on the functional group present. There
    are three different types of interactions, shown
    below in order of increasing strength
  • van der Waals forces (London Dispersion)
  • dipole-dipole interactions
  • hydrogen bonding

24
Intermolecular Forcesvan der Waals Forces or
London Forces
  • They are weak interactions caused by momentary
    changes in electron density in a molecule.
  • They are the only attractive forces present in
    nonpolar compounds.

Even though CH4 has no net dipole, at any one
instant its electron density may not be
completely symmetrical, resulting in a temporary
dipole. This can induce a temporary dipole in
another molecule. The weak interaction of these
temporary dipoles constituents van der
Waals forces.
25
van der Waals Forces-Surface Area
  • All compounds exhibit van der Waals forces.
  • The surface area of a molecule determines the
    strength of the van der Waals interactions
    between molecules. The larger the surface area,
    the larger the attractive force between two
    molecules, and the stronger the intermolecular
    forces.

26
van der Waals Forces-Polarizability
  • van der Waals forces are also affected by
    polarizability.
  • Polarizability is a measure of how the electron
    cloud around an atom responds to changes in its
    electronic environment.

Larger atoms, like iodine, which have more
loosely held valence electrons, are more
polarizable than smaller atoms like fluorine,
which have more tightly held electrons.
27
Intermolecular ForcesDipole-Dipole Interactions
  • Dipoledipole interactions are the attractive
    forces between the permanent dipoles of two polar
    molecules.
  • Consider acetone (below). The dipoles in adjacent
    molecules align so that the partial positive and
    partial negative charges are in close proximity.
    These attractive forces caused by permanent
    dipoles are much stronger than weak van der Waals
    forces.

28
Intermolecular ForcesHydrogen Bonding
  • Hydrogen bonding typically occurs when a hydrogen
    atom bonded to O, N, or F, is electrostatically
    attracted to a lone pair of electrons on an O, N,
    or F atom in another molecule.

29
Summary of Intermolecular Forces
Note as the polarity of an organic molecule
increases, so does the strength of its
intermolecular forces.
30
Physical Properties of Organic Molecules
31
Quiz Review
  • Tuesday 5-6 pm
  • Wednesday 3-4 pm
  • Thursday 6-650am
  • You may come to one or all review sessions.
  • Bring questions. (No Questions-No Review)
  • If you can not make it to any of the review time
    then see me at my office hours.

32
Boiling Point
  • The boiling point of a compound is the
    temperature at which liquid molecules are
    converted into gas.
  • In boiling, energy is needed to overcome the
    attractive forces in the more ordered liquid
    state.
  • The stronger the intermolecular forces, the
    higher the boiling point.
  • For compounds with approximately the same
    molecular weight

33
Comparing Boiling Points-molecules w/ different
functional groups
Consider the example below. Note that the
relative strength of the intermolecular forces
increases from pentane to butanal to 1-butanol.
The boiling points of these compounds increase in
the same order.
  • For two compounds with similar functional groups
  • The larger the surface area, the higher the
    boiling point.
  • The more polarizable the atoms, the higher the
    boiling point.

34
Comparing Boiling Points-molecules w/ different
functional groups
Consider the examples below which illustrate the
effect of size and polarizability on boiling
points.
35
Separation of Molecules by Boiling Point
Liquids having different boiling points can be
separated in the laboratory using a distillation
apparatus, shown in Figure 3.4.
36
Melting Point
  • The melting point is the temperature at which a
    solid is converted to its liquid phase.
  • In melting, energy is needed to overcome the
    attractive forces in the more ordered crystalline
    solid.
  • The stronger the intermolecular forces, the
    higher the melting point.
  • Given the same functional group, the more
    symmetrical the compound, the higher the melting
    point.

37
Melting Point
  • Because ionic compounds are held together by
    extremely strong interactions, they have very
    high melting points.
  • With covalent molecules, the melting point
    depends upon the identity of the functional
    group. For compounds of approximately the same
    molecular weight

38
Melting Point Trends
  • The trend in melting points of pentane, butanal,
    and 1-butanol parallels the trend observed in
    their boiling points.

39
The Symmetry of a Molecule Determines its Melting
Point
  • A compact symmetrical molecule like neopentane
    packs well into a crystalline lattice whereas
    isopentane, which has a CH3 group dangling from a
    four-carbon chain, does not. Thus, neopentane has
    a much higher melting point.

40
Solubility
  • Solubility is the extent to which a compound,
    called a solute, dissolves in a liquid, called a
    solvent.
  • In dissolving a compound, the energy needed to
    break up the interactions between the molecules
    or ions of the solute comes from new interactions
    between the solute and the solvent.

41
Solubility-comparing properties of solvents and
solutes
  • Compounds dissolve in solvents having similar
    kinds of intermolecular forces.
  • Like dissolves like.
  • Polar compounds dissolve in polar solvents.
    Nonpolar or weakly polar compounds dissolve in
    nonpolar or weakly polar solvents.
  • Water is very polar solvent (forms hydrogen bonds
    with solutes).
  • Most ionic compounds are soluble in water, but
    insoluble in organic solvents.
  • Many organic solvents are either nonpolar, like
    carbon tetrachloride (CCl4) and hexane
    CH3(CH2)4CH3, or weakly polar, like diethyl
    ether (CH3CH2OCH2CH3).

42
Solubility-dissolving ionic compounds
  • To dissolve an ionic compound, the strong ion-ion
    interactions must be replaced by many weaker
    ion-dipole interactions.

43
Solubility-the five carbon rule for organic
compounds
  • An organic compound is water soluble ONLY if it
    contains one polar functional group capable of
    hydrogen bonding with the solvent for every five
    C atoms it contains.
  • For example, compare the solubility of butane and
    acetone in H2O and CCl4.

44
Solubility-organic compounds which are soluble in
water
  • Since butane and acetone are both organic
    compounds, they are soluble in the organic
    solvent CCl4. Butane, which is nonpolar, is
    insoluble in H2O. Acetone is soluble in H2O
    because it contains only three C atoms and its O
    atom can hydrogen bond with an H atom of H2O.

45
Organic Molecules which are not Water soluble
  • Cholesterol has 27 carbon atoms and only one OH
    group. Its carbon skeleton is too large for the
    OH group to solubilize by hydrogen bonding, so
    cholesterol is insoluble in water.

46
Solubility
  • The nonpolar part of a molecule that is not
    attracted to H2O is said to be hydrophobic.
  • The polar part of a molecule that can hydrogen
    bond to H2O is said to be hydrophilic.
  • In cholesterol, for example, the hydroxy group is
    hydrophilic, whereas the carbon skeleton is
    hydrophobic.

47
(No Transcript)
48
(No Transcript)
49
ApplicationSoap
Soap Soap molecules have two distinct partsa
hydrophilic portion composed of ions called the
polar head, and a hydrophobic carbon chain of
nonpolar CC and CH bonds, called the nonpolar
tail.
50
The Cell Membrane
51
Ionophores
  • Transport Across a Cell Membrane
  • Polar molecules and ions are transported across
    cell membranes encapsulated within molecules
    called ionophores.
  • Ionophores are organic molecules that complex
    cations. They have a hydrophobic exterior that
    makes them soluble in the nonpolar interior of
    the cell membrane, and a central cavity with
    several oxygens whose lone pairs complex with a
    given ion.

52
Transport Across a Cell Membrane
53
Crown Ethers
Several synthetic ionophores have also been
prepared, including one group called crown
ethers. Crown ethers are cyclic ethers
containing several oxygen atoms that bind
specific cations depending on the size of their
cavity.
54
Vitamins
  • Vitamins are either fat or water soluble.
  • Vitamin A - is fat soluble and water insoluble
  • Contains one hydroxyl per 20 carbons
  • Vitamine C - is Water soluble
  • Contains 4 hydroxyl groups and a carbonyl group
    per 6 carbons.
Write a Comment
User Comments (0)
About PowerShow.com