Draw structures for all constitutional isomers with the molecular formula C4H8 that have:
(a) Only single bonds (b) One double bond

(a)

(b)

Refer to the diagram attached for the structures.

Explanation:

Calculate the degree of unsaturation to find the number of rings and multiple bonds (including double bonds) in those isomer molecules. The presence of each ring and each double bond would add one to the degree of unsaturation of that molecule.

Let , , , and denote the number of carbon, nitrogen, halogen, and hydrogen atoms in each isomer molecule, respectively.

The degree of unsaturation of one such molecule would be:

.

For :

Therefore, the degree of unsaturation of a molecule with the chemical formula would be:

.

In other words, the degree of unsaturation is for all isomers with this particular chemical formula. Therefore, each isomer would contain either a ring or a double bond, but not both.

If there is no double bond in one such molecule, there must be exactly one ring per molecule.

The minimum number of carbon atoms in a ring is three. With four carbon atoms in each molecule, there would be either a three-member ring (with one methyl group attached) or a four-member ring.

If there is one double bond in one such isomer molecule, there would not be a ring. Because of the degree of unsaturation, there would be no more than one double bond in each of these molecules.

With four carbon atoms, there are two possible backbones to consider: backbones with three carbon atoms each, and backbones with four carbon atoms each.

The backbone of those molecules might contain three carbon atoms. There would be one double bond in the backbone and one methyl group attached to the carbon atom at the center of the backbone. The corresponding isomer molecule would be 2-methyl-1-propene.

Alternatively, the backbone of those molecules might contain four carbon atoms. There are two possible locations for the double bond:

Notice, that the name 2-Butene refers to two distinct spatial isomers. Unlike carbon-carbon single bonds, groups on the two sides of a carbon-carbon double bond are unable to rotate relative to one another. Therefore, the first and fourth carbon atoms would either be:

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."