```python
def field_of(record, field):
    if field not in record:
        raise ValueError(f"Field '{field}' not found in record")
    return record[field]

def sort_pairs(records, field):
    return sorted(records, key=lambda x: x[field])
```

This solution redefines the `field_of` and `sort_pairs` functions as required. It uses Python's built-in `sorted` function with a custom key that accesses the specified field of each record. The function checks for missing fields by raising a `ValueError`, adhering to the contract.