Which of the following is TRUE for alkenes?
Which of the following is TRUE for alkenes?
The correct options are
A Alkenes have pi bonds (not all bonds)
B Alkenes are more reactive than alkanes
C Alkenes, especially the higher ones with 3 or more carbons can possibly exhibit geometrical isomerism
D Alkenes are soluble in organic solvents
Physical properties of alkenes are almost similar to that of alkanes.
Do you remember physical properties of hydrocarbons?
PHYSICAL PROPERTIES OF HYDROCARBONS
Hydrocarbons are almost non-polar molecules. Therefore, the intermolecular forces of attraction are of van der Walls type, which mainly depends on the shape and, hence, on the structure of the molecule. These forces depend on the surface area of the contact between adjacent molecules. Greater the surface area, stronger are the van der Waals forces of attraction.
a. Boiling point Among the straight-chain alkanes, C1−C4 are gases, C5—C17 are liquids, and C18 onwards are colourless, waxy solids. Boiling point increases with increase in the carbon content due to the increase in surface area, and, hence, van der Waals forces of attraction and the boiling point increase.
Branched-chain isomers Shave lower boiling point than corresponding n-alkalies. Due to the decrease in surface. area, van der Waals forces of attraction minimize and the boiling point decreases. For example. Boiling points of n.-pentane, isopentane, and neopentane are 309, 301, and 282.5 K, respectively.
c. Solubility: 'Like dissolves like' is the general rule of solubility. Hydrocarbons are insoluble in polar solvents such as H2O and alcohol, but highly soluble in non-polar solvents such non-polar as petroleum, ether, benzene,. and CCl4.
d. Density: The densities of alkanes increase with increase in molecular masses till the limiting value of about 0.8 gm cm−3 is reached. This means that all alkanes are lighter than water. Like alkanes, alkenes and alkynes also have a maximum density of about 0.89 gm cm−3. Therefore, all hydrocarbons are lighter than H2O.
e. Reactivity of hydrocarbons: Since (C—C) and (C—H) a-bonds are quite strong, alkanes are the least reactive hydrocarbons. That is why they are called paraffins (Latin parum means little and affinis means affinity or reactivity).
A Alkenes have pi bonds (not all bonds)
B Alkenes are more reactive than alkanes
C Alkenes, especially the higher ones with 3 or more carbons can possibly exhibit geometrical isomerism
D Alkenes are soluble in organic solvents
Physical properties of alkenes are almost similar to that of alkanes.
Do you remember physical properties of hydrocarbons?
PHYSICAL PROPERTIES OF HYDROCARBONS
Hydrocarbons are almost non-polar molecules. Therefore, the intermolecular forces of attraction are of van der Walls type, which mainly depends on the shape and, hence, on the structure of the molecule. These forces depend on the surface area of the contact between adjacent molecules. Greater the surface area, stronger are the van der Waals forces of attraction.
a. Boiling point Among the straight-chain alkanes, C1−C4 are gases, C5—C17 are liquids, and C18 onwards are colourless, waxy solids. Boiling point increases with increase in the carbon content due to the increase in surface area, and, hence, van der Waals forces of attraction and the boiling point increase.
Branched-chain isomers Shave lower boiling point than corresponding n-alkalies. Due to the decrease in surface. area, van der Waals forces of attraction minimize and the boiling point decreases. For example. Boiling points of n.-pentane, isopentane, and neopentane are 309, 301, and 282.5 K, respectively.
c. Solubility: 'Like dissolves like' is the general rule of solubility. Hydrocarbons are insoluble in polar solvents such as H2O and alcohol, but highly soluble in non-polar solvents such non-polar as petroleum, ether, benzene,. and CCl4.
d. Density: The densities of alkanes increase with increase in molecular masses till the limiting value of about 0.8 gm cm−3 is reached. This means that all alkanes are lighter than water. Like alkanes, alkenes and alkynes also have a maximum density of about 0.89 gm cm−3. Therefore, all hydrocarbons are lighter than H2O.
e. Reactivity of hydrocarbons: Since (C—C) and (C—H) a-bonds are quite strong, alkanes are the least reactive hydrocarbons. That is why they are called paraffins (Latin parum means little and affinis means affinity or reactivity).
