Question

Explain the difference between (a) linear and branched polyethylene. (b) glucose and fr?ctose. (c) maltose and sucrose

Short answer

Short Answer: Linear polyethylene (HDPE) has a regular structure with closely packed chains, while branched polyethylene (LDPE) has an irregular structure with side branches affecting the material's properties. Glucose and fructose are both monosaccharides with different molecular structures - glucose is an aldohexose sugar and fructose is a ketohexose sugar. Maltose and sucrose are disaccharides formed by different combinations of monosaccharides - maltose consists of two glucose units with an alpha 1-4 linkage, while sucrose consists of one glucose and one fructose unit with an alpha 1-2 linkage.

Step-by-step solution

(a) Linear vs. Branched Polyethylene

Linear and branched polyethylene are both forms of polymers made from the same monomer (ethylene), but they have different structures due to the arrangement of their molecules. Linear polyethylene (also known as high-density polyethylene, or HDPE) consists of long, straight chains of ethylene molecules connected with each other in a regular pattern. The chains are closely packed, resulting in a high density and crystallinity, which means their physical properties such as tensile strength, stiffness, chemical resistance, and temperature resistance are generally better than those of branched polyethylene. Linear polyethylene is mainly used in piping, bottles, and containers. Branched polyethylene (also known as low-density polyethylene, or LDPE) has a more irregular structure, with side branches connected to the main chain. The presence of branches affects the material's properties: the chains are less tightly packed, resulting in a lower density and crystallinity. Therefore, branched polyethylene has inferior physical properties to linear polyethylene, such as lower tensile strength, stiffness, and temperature resistance. However, branched polyethylene has a higher degree of elasticity and is more flexible compared to linear polyethylene. Branched polyethylene is commonly used in films, plastic bags, and other flexible applications.

(b) Glucose vs. Fructose

Glucose and fructose are monosaccharides, which are the simplest form of carbohydrates with a single sugar unit. Their molecular formula is the same (C6H12O6), but their molecular structures and configurations are different, making them distinct sugars. Glucose is an aldohexose sugar, which means it has an aldehyde group (-CHO) and six carbon atoms. Its structure can be either a linear chain or a cyclic form when the aldehyde group reacts with a hydroxyl group from another carbon atom, forming a six-membered ring called a pyranose. Fructose is a ketohexose sugar, which means it has a ketone group (>C=O) and six carbon atoms. Similar to glucose, fructose can form a cyclic structure, but it forms a five-membered ring called furanose due to the reaction between the ketone group and a hydroxyl group from another carbon atom. These differences between glucose and fructose cause them to have different properties, such as sweetness and reactivity. Fructose is often considered to be sweeter than glucose, and they participate in different chemical reactions due to their distinct functional groups.

(c) Maltose vs. Sucrose

Maltose and sucrose are both disaccharides, which are carbohydrates consisting of two monosaccharide units joined together by a glycosidic bond. Maltose, also known as malt sugar, is formed by the combination of two glucose molecules. The glycosidic bond between the glucose units is an alpha (α) 1-4 linkage, meaning that the bond is formed between the first and fourth carbon atoms. Maltose can be found in malted grains or produced during the hydrolysis of starch. Sucrose, commonly known as table sugar, is formed by the combination of one glucose molecule and one fructose molecule. The glycosidic bond between these sugar units is an alpha (α) 1-2 linkage, meaning that the bond is formed between the first carbon atom of glucose and the second carbon atom of fructose. Sucrose is found naturally in many plants, including sugar cane and sugar beet, and it is the most commonly used sugar in food production. The differences between maltose and sucrose lie in the monosaccharides involved in their formation and the type of glycosidic bond that connects them. These differences result in distinct properties, such as sweetness and their behavior in reactions.

Key concepts

polyethylene

Polyethylene is a type of polymer that is widely used due to its versatile properties. A polymer is essentially a large molecule composed of repeated smaller units called monomers. In the case of polyethylene, the monomer is ethylene. Depending on how these ethylene units or chains are arranged, polyethylene can either be linear or branched.

• Linear Polyethylene: Also known as High-Density Polyethylene (HDPE), linear polyethylene is composed of long, straight chains of ethylene without any branching. Because the chains are closely packed, HDPE has high density, crystallinity, tensile strength, and resistance to chemicals and temperature. This makes it ideal for applications like making pipes, bottles, and containers.


• Branched Polyethylene: In Low-Density Polyethylene (LDPE), branches grow from the main chain of ethylene units. These branches result in a loosely packed structure, lowering the material's density and crystallinity. While this makes LDPE less strong and resistant compared to HDPE, it gives the material greater flexibility and elasticity. This is why LDPE is often used for films, plastic bags, and other flexible items.

monosaccharides

Monosaccharides are the simplest form of carbohydrates, consisting of single sugar units. They play crucial roles in metabolism, providing energy and serving as building blocks for more complex molecules. Two common monosaccharides are glucose and fructose, both with the molecular formula C₆H₁₂O₆, yet they differ in structure.

• Glucose: This sugar is an aldohexose, meaning it has an aldehyde group and six carbon atoms. It can exist in a linear chain form or a cyclic form. In its cyclic form, an aldehyde group reacts with a hydroxyl group, creating a six-membered ring called pyranose. Glucose is an essential energy source for cells.


• Fructose: Known as a ketohexose, fructose has a ketone group instead of an aldehyde group. It also forms a cyclic structure, but as a five-membered ring called furanose. This difference gives fructose a unique reactivity and sweetness profile, often making it sweeter than glucose.

disaccharides

Disaccharides are carbohydrates made of two monosaccharide units connected by a glycosidic bond. They serve both as energy sources and as structural components in various organisms. Maltose and sucrose are two well-known disaccharides, differing in their monosaccharide components and types of linkage.

• Maltose: Often referred to as malt sugar, maltose consists of two glucose molecules bonded together. The bond, known as an alpha (α) 1-4 glycosidic linkage, connects the first carbon of one glucose to the fourth carbon of the adjacent glucose. Maltose is naturally found in malted grains and is a byproduct of starch digestion.


• Sucrose: Commonly known as table sugar, sucrose is formed from one glucose and one fructose molecule. An alpha (α) 1-2 glycosidic bond links the first carbon of glucose to the second carbon of fructose. Besides being a major sweetener in foods, sucrose is also found naturally in sugar beet, sugar cane, and other plants.