What are dienes? Briefly discuss their properties and system of nomenclature.

Dienes are a class of organic compounds that contain two carbon-carbon double bonds, often represented with the general formula C_nH_2n-2. These molecules can be classified into two categories: conjugated dienes and non-conjugated dienes. Conjugated dienes have alternating single and double bonds, while non-conjugated dienes have their double bonds separated by two or more single bonds.

Dienes exhibit a range of interesting chemical properties, which include: a) Greater reactivity: Due to the presence of double bonds, dienes are generally more reactive than their corresponding alkanes and alkenes. This increased reactivity is attributed to the pi electrons in the double bonds, which can be easily shared or removed. b) UV absorption: Dienes can absorb ultraviolet (UV) light, resulting in an electronic transition of their pi electrons to higher energy levels. This property is employed in various applications, such as UV spectroscopy and sunscreens. c) Polymerization: Dienes can undergo polymerization, leading to the formation of high molecular weight polymers. This process is particularly important in the production of synthetic rubber and plastic materials. d) Susceptible to electrophilic addition reactions: Dienes readily undergo electrophilic addition reactions, which involve the addition of an electrophile to the double bond. These reactions can lead to a variety of chemical products, depending on the specific electrophile and reaction conditions.

The system of nomenclature for dienes is largely based on the guidelines established by the International Union of Pure and Applied Chemistry (IUPAC). When naming dienes, the following steps are followed: a) Identify the parent hydrocarbon chain: Select the longest continuous chain of carbon atoms that contains both double bonds, and determine the corresponding alkane name. b) Replace the "ane" suffix with "adiene": This indicates the presence of two double bonds in the molecule. c) Number the carbon atoms in the parent chain: Assign the lowest possible numbers to the double bond-containing carbons. In conjugated dienes, one double bond will always have a lower number than the other. d) Add substituent names and positions: If there are any substituents attached to the parent chain, list them in alphabetical order, along with their numerical positions, as prefixes. Use commas to separate numbers and hyphens to separate numbers from words. For example, for the molecular formula CH2=C(CH3)HC=CH2, the IUPAC name would be 3-methyl-1,3-pentadiene.