None of these syllables are pronounced with an 'e' as in 'red'. Unstressed syllables are either pronounced with an /ɪ/, as 'pit' or schwa /ə/. The closest sound to the schwa is the 'u' sound in 'cup', but it's shorter and weaker. There are no fixed rules as to which of these sounds are used - sometimes it's just personal choice. This is how I'd pronounce these words: 1.diamond / 'dai mənd/ ---> schwa in second (unstressed) syllable 2.elephant / 'el ɪ fənt/ ---> /ɪ / in middle syllable, schwa in third 3.purpose /ˈpɜː.pəs/ ---> schwa in second (unstressed) syllable 4.stratum / 'stra: təm/ ----> schwa in second (unstressed) syllable 5.basket / 'ba:skɪt/ ----> /ɪ / in second (unstressed) syllable 6.culprit /ˈkʌl prɪt/ ----> /ɪ / in second (unstressed) syllable

Are you talking about the "o" in "diamond"? It's actually the third syllable. If I was saying it slowly I would say it with the sound in "red", but when said at normal speed it comes out as a schwa sound. For every other one except "elephant", my answer is the same - I'd use an "e" when pronouncing the word very slowly, but at normal speed it should be a schwa. For "elephant", the second "e" is pronounced with neither of those sounds. The first "e" is pronounced with the "e" in "red", the second one is pronounced with the "u" in "cut", and the "a" is pronounced with a schwa sound.

Technically, the last vowel should be /ə/, but /ɪ/ (pit) is so close that you could pronounce it that way without causing any problems (as long as it remains unstressed)! To be honest, for me pronouncing the last vowel in those words as /e/ (red) sounds extremely unnatural.