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Any molecule that has a nonzero vector sum of dipole moments is said to be polar and have a dipole moment
A dipole moment refers to slight opposite charges on opposite sides of a bond. The resulting bond is said to be polar; it has a positive pole and a negative pole, much like a bar magnet.
In order to determine if a particular bond is polar or not, one must look for the electronegativity of each atom. Pauling's electronegativity is a measure of how strong a particular atom pulls electrons towards it in a bond. The value of the difference between their electronegativities (
Consider the bonds in
There is one oxygen bonded to two hydrogens in one water molecule. Based on the difference in electronegativites for the bonds, it is clearly a polar molecule
In the figure above, the
Notice that the water molecule has an overall dipole moment that points straight up towards the oxygen. This is because a dipole moment of a molecule depends on the vector sum of the bond dipoles.
As you can see, the
Here's what I get.
When there is more than one permissible IUPAC name, the first name is preferred.
There are two systems of IUPAC names for ethers.
1. Substitutive names.
The ethers are named as alkoxyalkanes, with the senior component selected as the parent compound.
2. Functional group names.
The ethers are named as alkyl alkyl ethers, with the alkyl groups in alphabetical order followed by the class name ether, each as a separate word.
Esters are named as alkyl alkanoates.
The name of the alkyl group is written first, followed by the name of the acid with the ending -ic acid replaced by the ending -ate.
There are three systems of IUPAC names for nitriles.
1. As alkanenitriles.
The ending -nitrile is added to the name of the alkane with the same number of carbon atoms.
2. If the compound is considered to be formed from a carboxylic acid with a "trivial name" (
3. As alkyl cyanides.
The name of the alkyl group precedes the class name cyanide.
It can be considered as basically spatial crowding.
Steric hindrance is a kinetic factor that limits the ease to which a nucleophile (electron pair donor) can approach an electrophile (electron pair acceptor).
As an example, consider the reaction seen below, which one might hope is
Here, the nucleophile is cyanide (
We should predict that reaction does not work via an
(LEFT: steric hindrance; RIGHT: reduced steric hindrance)
That reduces the ease to which a successful collision can occur between two reactants, and slows down the first step in a given substitution mechanism (making it the rate-limiting step).
Hence, this reaction proceeds more easily as a first-order mechanism (e.g.
The rate law for this could then be approximated as first-order based on the slow step, since it dominates the extent of the reaction time:
#r(t) ~~ k_1["Br"^(-)]#
(Depending on the choice of solvent, either
You'll have to be able to draw these out to name them. It is impossible to name by inspection of their chemical formulas.
I've highlighted the longest hydrocarbon chain, which you would have had to identify.
Now you simply count from each end to determine the lowest possible set of carbon indices, and account for duplicate functional groups using prefixes. Alphabetize them afterwards.
NOTE: the smallest index should be the first point of difference between two sets of numberings.
There are four methyl groups in
#(a)#, while there is one methyl and one ethyl group in #(b)#.
Counting from the left:
#(a)#is then denoted #ul"2,2,3,3-tetramethylhexane"#.
#(b)#is then denoted #"3-ethyl-6-methylheptane"#.
Counting from the right:
#(a)#is then denoted #"4,4,5,5-tetramethylhexane"#.
#(b)#is then denoted #ul"5-ethyl-2-methylheptane"#.
The first name for
The second name for
The compound is 3-methyl-2-butanone.
To begin with the IR-abosorption,
The molecule of
Then, let's proceed to the NMR spectrum.
 A peak near
 A peak at
 The fact that the peak at
Therefore, the structure will be
Let's check the answer:
Here is a chemical shift table.(PDF)
Warning! Long Answer. The compound is propionic anhydride.
You know the formula is
An alkane with six carbon atoms has the formula
The degree of unsaturation
Therefore, the compound contains two rings and/or double bonds.
The spectrum has 10 protons and only two peaks. The molecule must have a symmetrical structure.
A peak with 2 neighbours and aone with 3 neighbors corresponds to an ethyl group (
However, I think you have the assignments reversed. The methyl group should have the smaller chemical shift.
A methyl group is normally at 0.9 ppm. Something is pulling it downfield
to 1.2 ppm.
A methylene group is normally at 1.3 ppm. Something is pulling it downfield
to 2.5 ppm.
We see from the table that a
We could expect a similar 1.3 ppm shift for a
This is just where the
We now know that the partial structure is
These fragments add up to
There is only one
The compound is propionic anhydride.
1. The compound has two double bonds.
We should expect to see
We see peaks at 8 ppm, 28 ppm, and 170 ppm. This is consistent with propionic anhydride.
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