Dynamically assigning projects property name to variable within a class

public class connClass

 {

     NpgsqlConnection conn = new NpgsqlConnection(projectName.Properties.Settings.Default.ConnString);

 }

String connStr = ConfigurationManager.ConnectionStrings["DefaultConnStr"].ConnectionString;

<configuration>
    <connectionStrings>
         <add name="DefaultConnStr" connectionString="Data Source=127.0.0.1..."/>
    </connectionStrings>
</configuration>

ConfigurationManager.AppSettings["PROJECT_NAME"];