Question

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

Short answer

Answer: (a) Linear polyethylene (HDPE) has a linear chain-like structure with no branching or side chains, resulting in higher density and greater strength, stiffness, and resistance to heat and chemicals, while branched polyethylene (LDPE) has an irregular structure with branching or side chains, leading to lower density, lower strength and stiffness, but higher flexibility. (b) Glucose is an aldohexose with an aldehyde functional group (CHO), while fructose is a ketohexose with a ketone functional group (CO), leading to different sweetness levels and metabolic processes. (c) Maltose is composed of two glucose molecules connected by an alpha-1,4 glycosidic linkage, while sucrose is composed of one glucose and one fructose molecule connected by an alpha-1,2 glycosidic linkage, resulting in different sweetness levels and characteristics.

Step-by-step solution

(a) Linear and Branched Polyethylene

Polyethylene is a type of polymer that consists of long chains of ethylene monomers. There are two main types of polyethylene: linear and branched polyethylene. The primary difference between these two types lies in their structural configuration. Linear polyethylene, also known as high-density polyethylene (HDPE), has a linear chain-like structure with no branching or side chains. This configuration allows the chains to pack closely together, resulting in a higher density compared to branched polyethylene. Linear polyethylene has stronger intermolecular forces, which provide greater strength, stiffness, and resistance to heat and chemicals. Branched polyethylene, also known as low-density polyethylene (LDPE), has a more irregular structure, with the presence of branching or side chains. These branches disrupt the close packing of chains, resulting in a lower density compared to linear polyethylene. Branched polyethylene has weaker intermolecular forces, which result in lower strength, stiffness, and resistance to heat and chemicals, but it possesses higher flexibility and is easier to process.

(b) Glucose and Fructose

Both glucose and fructose are monosaccharides, which are simple sugars or the most basic units of carbohydrates. The main difference between glucose and fructose lies in their chemical structure and properties. Glucose has a chemical formula of C6H12O6 and is an aldohexose, meaning it possesses an aldehyde functional group (CHO). Its linear structure consists of six carbons, with the CHO group at the first carbon atom and five hydroxyl groups (OH) attached to the remaining carbons. In its most stable cyclic form, glucose exists as an intramolecular hemiacetal. Fructose also has a chemical formula of C6H12O6, but it is a ketohexose, meaning it possesses a ketone functional group (CO). Its linear structure consists of six carbons, with the CO group at the second carbon atom and five hydroxyl groups (OH) attached to the other carbons. In its most stable cyclic form, fructose exists as an intramolecular hemiketal. The differing functional groups result in different sweetness levels and metabolic processes for glucose and fructose. Fructose is sweeter than glucose and is mainly metabolized in the liver, whereas glucose is less sweet and is directly used by cells for energy.

(c) Maltose and Sucrose

Both maltose and sucrose are disaccharides, which are formed when two monosaccharides are joined together. The primary difference between maltose and sucrose lies in their composition and characteristics. Maltose, also known as malt sugar, is composed of two glucose monosaccharide units joined together by an alpha-1,4 glycosidic linkage. This bond is formed when the first carbon of one glucose molecule bonds with the fourth carbon of another glucose molecule. Maltose is easily hydrolyzed back into two glucose molecules by the enzyme maltase, and it is less sweet than sucrose. Sucrose, commonly known as table sugar, is formed through the combination of one glucose monosaccharide and one fructose monosaccharide, which are joined together by an alpha-1,2 glycosidic linkage. This bond is formed when the first carbon of the glucose molecule bonds with the second carbon of the fructose molecule. Sucrose is also easily hydrolyzed back into glucose and fructose by the enzyme sucrase and is considerably sweeter than maltose.