Organic Chemistry: FUNCTIONAL GROUPS

Functional groups are certain groups of atoms within a molecule which determine the characteristics of that particular molecule. They are the most reactive part of the molecule.  Also, the same functional groups go through similar if not same chemical reactions whether the same size or not. But it's reactivity can change as a result of nearby functional groups.

The functional groups we focused especially on in class were: Alcohols, Halides (aka Halogens) and Nitro, Aldehydes, and finally Ketones.

Alcohols
-contain the -OH functional group
-are organic and form on saturated carbons
-are found in alcoholic drinks

To name alcohols, we simply replace the ending of the parent hydrocarbon with "ol". We also use the longest Carbon chain including the OH functional group.
Note: Always look for the name with the lowest number for the alcohol.

Examples:

Some properties of alcohols:

-parts of it are soluble, parts of it are insoluble

- smaller alcohols are soluble in water

-poisonous to some degree

If there is more than one OH group, then add the endings -diol, triol, etc to the parent hydrocarbon.

Halides and Nitro

These are attached to alkanes, alkynes and alkenes.

The most common ones are:

F= fluoro

Cl= chloro

Br= bromo

I= iodo

NO2= nitro

Here are some examples:

To name halides, we use the same rules as alkanes, alkenes and alkynes except at the beginning, we put the position and number of which halide or nitro present in the molecule as shown above. If there is more than 1 of the same type of halide, we use the prefixes -di, -tri, -tetra, etc.

Properties of Halides:

-usually insoluble in water

Properties of Nitro Compounds:

-insoluble in water

-unreactive, unless under drastic conditions

-are pretty explosive, but at least they smell good!

AldehydesThis funtional group includes a double conded oxygen on one side and an alkyl group on the other.

The oxygen must be on at the end of the chain, or else it is called a Ketone. Aldehydes are generally very reactive and somewhat soluble in water.

The ending of aldehydes is -al  (from aldehyde)

Examples:

 

Ketones

These are similar to aldehydes, except the oxygen is double-bonded somewhere in the middle of the molecule.
 

The ending for this functional group is -one. To name this group, find the lowest number of the oxygen, just like the aldehydes.  Ketones are usually unreactive.

Here are some examples:



**Start studying for the Chem 11 final next week! **

Lewis Structure

How to draw Lewis Diagrams

An outline of how to detemine the "best" Lewis structure for an example, NO₃^- is given below:

1.  Determine the total number of valence electrons in a molecule

2.  Draw a skeleton for the molecule which connects all atoms using only single bonds.  In simple molecules, the atom with the most available sites for bondng is usually placed central.  The number of bonding sites is detemined by considering the number of valence electrons and the ability of an atom to expand it's octet.  As you become better, you will be able to recognise that certain groups of atoms prefer to bond together in a certain way.

3.  Of the 24 valence electrons in NO₃^-, 6 were required to make the skeleton. Consider the remaining 18 electrons and place them so as to fill the ocets of as many atoms as possible (start with the most electronegative atoms first then proceed to the more electropositive atoms).

4.  Are the octets of all the atoms filled?   If not then fill the remaining octets by making multiple bonds (make a lone pair of electrons, located on a more electronegative atom, into a bonding pair of electrons that is shared with the atom that is electron defficient).

5.  Check that you have the lowest FORMAL CHARGES possible for all the atoms, without violating the octet rule;       (valence e-) - (1/2 bonding e-) - (lone electrons).

IMPORTANT : no Lewis diagram is complete without formal charges.  Lewis diagrams are drawn to examine mechanisms so knowing which parts of a molecule are electron defficient (+) and which are electron rich (-) is vital.
It is best to have a formal charge of 0 for as many of the atoms in a structure as possible.
If a formal charge of 1- is located next to a formal charge of 1+, the formal charges can usually be minimized by having a lone pair of electrons, located on the atom with the 1- charge become a bonding pair of electrons that is shared with the atom that has the 1+ formal charge (this can be visualised in the same way as the formation of multiple bonds were above). CAUTION : octets can be expanded to minimise formal charges but only for atoms in the second row of the periodic table  (where n=3 or greater).   For instance in our example, N cannot expand its octet so keeps a formal charge of 1+ and both singly bonded oxygens a formal charge of 1-.  If our molecule were SO₃ , however, it would be possible to minimize all formal charges by having the sulfur expand its octet.

6.  You may find that the best Lewis diagram (the one with the lowest formal charges and all octets satisfied) is given in a number of different ways.  For NO₃^-, three different diagrams are given below.  From left to right they start with the most complete Lewis diagram to the most simplified.

Why so many different ways?  Depends on the need of the chemist. For instance, complete structures are more useful for the novice organic chemist learning to appreciate the mechanism of a reaction while simplified versions may be preferred by inorganic chemists.

PRACTISE TIME!!
        PBr3

      N2H2

           

Bohr Model Diagram

Bohr Model Diagram

      While the Rutherford model focused on describing the nucleus, Niels Bohr turned his attention to describing the electron.  Prior to the Bohr Model, the accepted model was one which depicted the electron as an orbiting planet.  The flaw with the planet-like model is that an electron particle moving in a circular path would be accelerating (see circular motion).  An accelerating electron creates a changing magnetic field. This changing magnetic field would carry energy away from the electron, eventually slowing it down and allowing it to be "captured" by the nucleus.

For more information about Bohr Model Diagram, enjoy the video!

Electron Dot Diagrams

Electron Dot Diagrams

      The electrons in an atom’s outer energy level are the electrons that are important to consider in
chemical bonds and chemical reactions. These electrons can be represented in a diagram called an
electron dot diagram. The outermost electrons are drawn as dots around the chemical symbol.
In this activity, you will draw electron dot diagrams for several elements.

Procedure
1. Write the symbol for the element. For electron dot diagrams, this symbol represents the nucleus and all of the electrons of the atom except the outermost electrons. The symbol for chlorine is Cl. In an electron dot diagram, this symbol represents the nucleus and the ten electrons in the first two energy levels.
2. Use the periodic table to determine how many outer electrons the element has. Do this by finding to which group the element belongs.
Chlorine belongs to Group 17, the halogens, which have seven outer electrons.
3. Draw a dot to represent each electron in the outer level of the element. Two electrons can be placed on each side of the symbol. The first two electrons should be paired on the right side of the symbol. The rest of the outer electrons should be distributed counterclockwise one by one around the other sides of the symbol.

The electron dot diagram for chlorine is

                                                                              

1. ions (anions) are formed when an atom gains electrons.

2. Positive ions (cations) are formed when an atom loses electrons.

1. The overall charge on the compound must equal zero, that is, the number of electrons lost by one atom must equal the number of electrons gained by the other atom.

2. The Lewis Structure (electron dot diagram) of each ion is used to construct the Lewis Structure (electron dot diagram) for the ionic compound.

Lithium fluoride, LiF

1. Lithium atom loses one electron to form the cation Li⁺
2. Fluorine atom gains one electron to form the anion F^-
3. Lithium fluoride compound can be represented as



Li⁺ OR
1. In a covalent compound, electrons are shared between atoms to form a covalent bond in order that each atom in the compound has a share in the number of electrons required to provide a stable, Noble Gas, electronic configuration.

2. Electrons in the Lewis Structure (electron dot diagram) are paired to show the bonding pair of electrons.

3. Often the shared pair of electrons forming the covalent bond is circled

4. Sometimes the bond itself is shown (-), these structures can be referred to as valence structures.
 
ammonia, NH₃
1. Nitrogen atom has 5 valence electrons

2. Hydrogen atom has 1 valence electron

3. Each of the 3 hydrogen atoms will share its electron with nitrogen to form a bonding pair of electrons (covalent bond) so that each hydrogen atom has a share in 2 valence electrons (electronic configuration of helium) and the nitrogen has a share in 8 valence electrons (electron configuration of neon)

4. Lewis Structure (electron dot diagram) for ammonia



OR  MORE EXAMPLES

Chemical Bonding

Atoms are made of protons, neutrons, and electrons. Since bonding involves electrical attraction, it is the protons and electrons that are more important.

There are 2 types of chemical bondings:
1. Covalent bonding: a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds.

2. Ionic bonding: a kind of chemical bonding  formed by electrostatic attraction resulting when one atom gives valence electrons to another atom, resulting in filled energy shells for both atoms.

These two electrons are shared by two atoms to form covalent compound.

Fluorine needs one more electron to fill up its outer shell of electrons. Carbon will provide that electron as long as fluorine shares one of its electrons with carbon because carbon also wants to have eight outer electrons.
You can see how four fluorine atoms can connect to one carbon atom.  Carbon is partially positive because its outer electrons are closer to the fluorine atoms and not canceling out its own positive charge. For this reason, they call this a polar covalent bond. "Covalent" because the electrons are shared and "polar" because there's a + and - charge separation.





Convalent compounds can be classified to in polar bonding and nonpolar bonding.
1. Polar bonding:  Covalent compounds are said to be polar when the shared electron moves towards the atom with the greater mass.
- The atom towards which the electron pair shift gets a slight negative charge while the other atoms acquires s slight positive charge.
- The polar covalent molecules has two conters of charge and this is known as "dipole"
- There is a great difference is the electro negativity values of the atoms.

2. Non-polar bonding: Covalent compounds are said to be nonpolar when the shared pair of electrons are at an euqal distance from both the atoms invovled in bonding.
- There is no charge separation and the molecule is electrically neutral
- The eletronegativity difference between the atoms is 0.

Hydrogen atoms are attracted to each other. There's a balance of repulsion and attraction. With no attraction, atoms would never make a bond. With no repulsion, the atoms would just go together as one atom. So balancing attraction and repulsion allow for atoms to form compounds.

They are two fluorine atoms. The nucleus of the fluorine atom has nine protons. Two electrons orbit close to the nucleus. The outer seven spread out to maximize space between them. However there is still space for one more electron. See how the two electrons are being attracted by protons from both atoms. This pulls the atoms together, and because there is room, the atoms bond.

Here is a video found on YouTube about chemical bonding


Here is a good website to learn chemical bonding:
http://www.visionlearning.com/library/module_viewer.php?mid=55

Naming of Organic Chemistry 2

Now we have known how to name Alkanes.Now we are learning to name Alkenes & Alkynes(Don't be confused of them).

ALKENES

Alkenes are the chemical compounds which consist only of elements Carbon(C) and Hydrogen(H) .And alkanes are linked together only by double bonds.

In the same way, the ending of alkenes are "-ene".Don't be confused by alkanes and alkenes.

Here are two alkenes.

By them, we can easily know that the general formula for Alkenes is CnH2n.

Here is a example.

This is 1-hexene.

This is 4-methyl-1-hexene.

And this is 4-methyl-2-ethyl-1-hexene.

Trans & Cis butene

For alkenes, some molecules will have the same structure but different geometry.

The first one named cis-2-butene.The second one named trans-2-butene.

cis-WX or YZ

trans-WZ or XY

There is no need for cis or trans in the name:WY or XZ.

For example,

This is cis-3,4-dimethyl-3-hexene.

ALKYNES(don't be confused by alkanes, alkenes & alkynes)

Like alkanes and alkenes, the ending of alkynes are "-yne".The naming rules of alkynes are "mostly" like alkenes but no cis or trans.
The general formula for alkynes is CnH2n-2.

eg.Naming these alkynes.

1-butyne

5-methyl-2-hexyne.

Alkenes are the chemical compounds which consist only of elements Carbon(C) and Hydrogen(H) .And alkanes are linked together only by triple bonds.

Naming of Organic Chemistry 1

Organic chemistry plays an important part of the world.So it is also important for us to understand Organic chemistry.Let's start!

There are four general characteristics of Organic Compounds:
1.Low melting point;
2.Weak or Non-electrolytes;
3.Can link with other atoms in Single bonds, Double bonds & Triple bonds;

4.Can form chains of carbon atoms that are linked in a straight-line, circular pattern or branched pattern.

ALKANES(it is straight chain)

Alkanes are the chemical compounds which consist only of elements Carbon(C) and Hydrogen(H) .And alkanes are linked together only by single bonds.

Alkanes naming: the names of all hydrocarbons end in "-ane" .

Here are the names of Alkanes:

Methane CH4

Ethane C2H6

Propane C3H8

Butane C4H10

Pentane C5H12

Hexane C6H14

Heptane C7H16

Octane C8H18

Nonane C9H20

Decane C10H22

By them, we can easily know the general formula for writing the formula of an alkane is:CnH2n+2

Branched Hydrocarbons

Hydrocarbons can have branched which are also hydrocarbon chains.These hydrocarbons are called substituted hydrocarbons or branched hydrocarbons.

For example:

Carbon has 4 bonds

Four hydrogen atoms.

When a carbon is attached to one other carbons.

Three hydrogen atoms.

↓

Two hydrogen atoms.

↓

One hydrogen atom.

↓

Zero hydrogen atom!

Alkyl group:an alkane that has lost one hydrogen atom called alkyl.

Naming the names of all alkyl group end in "-yl".(it is because they are alkyls)

Use these:"di","tri","tetra",etc. when there are more than one of the same kind of alkyl group.

But if there are more than one kind of alkyl group, list them alphabetically, put its position number in front, put a dash between each alkyl group and its number.

Here's an example.

Both of them are C4H10. But they are different. The first one is butane.The second one is 2-methylpropane.

So now it is easy for you, isn't it?